Fix warning in losses_utils.py
Fix warning in losses_utils.py

While debugging 24577 I noticed the following warning:
```
WARNING:tensorflow:From /usr/local/lib/python3.6/dist-packages/tensorflow/python/keras/utils/losses_utils.py:170: to_float (from tensorflow.python.ops.math_ops) is deprecated and will be removed in a future version.
Instructions for updating:
Use tf.cast instead.
```

This fix fixes the warning.

Signed-off-by: Yong Tang <765086fe2e0c1f980161f127fec596800f327f62@outlook.com>

tensorflow/tensorflow-pywrap_tf_optimizer,ppwwyyxx/tensorflow,gautam1858/tensorflow,annarev/tensorflow,ageron/tensorflow,theflofly/tensorflow,frreiss/tensorflow-fred,paolodedios/tensorflow,freedomtan/tensorflow,xzturn/tensorflow,karllessard/tensorflow,tensorflow/tensorflow,karllessard/tensorflow,apark263/tensorflow,tensorflow/tensorflow,ppwwyyxx/tensorflow,paolodedios/tensorflow,DavidNorman/tensorflow,aldian/tensorflow,adit-chandra/tensorflow,xzturn/tensorflow,tensorflow/tensorflow,petewarden/tensorflow,Intel-Corporation/tensorflow,aldian/tensorflow,cxxgtxy/tensorflow,theflofly/tensorflow,tensorflow/tensorflow-pywrap_saved_model,tensorflow/tensorflow-pywrap_saved_model,adit-chandra/tensorflow,petewarden/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,tensorflow/tensorflow-pywrap_saved_model,renyi533/tensorflow,paolodedios/tensorflow,arborh/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,theflofly/tensorflow,Intel-Corporation/tensorflow,alsrgv/tensorflow,DavidNorman/tensorflow,adit-chandra/tensorflow,theflofly/tensorflow,petewarden/tensorflow,frreiss/tensorflow-fred,adit-chandra/tensorflow,davidzchen/tensorflow,davidzchen/tensorflow,Intel-tensorflow/tensorflow,frreiss/tensorflow-fred,tensorflow/tensorflow-pywrap_tf_optimizer,freedomtan/tensorflow,kevin-coder/tensorflow-fork,hfp/tensorflow-xsmm,apark263/tensorflow,paolodedios/tensorflow,jendap/tensorflow,jendap/tensorflow,aam-at/tensorflow,sarvex/tensorflow,gunan/tensorflow,renyi533/tensorflow,karllessard/tensorflow,gautam1858/tensorflow,annarev/tensorflow,jhseu/tensorflow,tensorflow/tensorflow-pywrap_saved_model,tensorflow/tensorflow-experimental_link_static_libraries_once,arborh/tensorflow,aam-at/tensorflow,DavidNorman/tensorflow,tensorflow/tensorflow-pywrap_saved_model,freedomtan/tensorflow,yongtang/tensorflow,kevin-coder/tensorflow-fork,annarev/tensorflow,ppwwyyxx/tensorflow,arborh/tensorflow,chemelnucfin/tensorflow,ghchinoy/tensorflow,xzturn/tensorflow,chemelnucfin/tensorflow,ppwwyyxx/tensorflow,apark263/tensorflow,yongtang/tensorflow,gunan/tensorflow,paolodedios/tensorflow,karllessard/tensorflow,yongtang/tensorflow,aam-at/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,petewarden/tensorflow,chemelnucfin/tensorflow,chemelnucfin/tensorflow,alsrgv/tensorflow,aldian/tensorflow,apark263/tensorflow,ghchinoy/tensorflow,ageron/tensorflow,yongtang/tensorflow,cxxgtxy/tensorflow,ppwwyyxx/tensorflow,tensorflow/tensorflow,xzturn/tensorflow,jhseu/tensorflow,jbedorf/tensorflow,theflofly/tensorflow,ageron/tensorflow,theflofly/tensorflow,ageron/tensorflow,gautam1858/tensorflow,yongtang/tensorflow,cxxgtxy/tensorflow,theflofly/tensorflow,sarvex/tensorflow,DavidNorman/tensorflow,freedomtan/tensorflow,ageron/tensorflow,karllessard/tensorflow,gunan/tensorflow,apark263/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,annarev/tensorflow,aldian/tensorflow,aam-at/tensorflow,alsrgv/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,renyi533/tensorflow,jbedorf/tensorflow,annarev/tensorflow,kevin-coder/tensorflow-fork,paolodedios/tensorflow,hfp/tensorflow-xsmm,kevin-coder/tensorflow-fork,gautam1858/tensorflow,xzturn/tensorflow,yongtang/tensorflow,Intel-Corporation/tensorflow,annarev/tensorflow,DavidNorman/tensorflow,renyi533/tensorflow,tensorflow/tensorflow,annarev/tensorflow,jbedorf/tensorflow,freedomtan/tensorflow,jhseu/tensorflow,DavidNorman/tensorflow,jhseu/tensorflow,arborh/tensorflow,davidzchen/tensorflow,Intel-Corporation/tensorflow,ageron/tensorflow,annarev/tensorflow,renyi533/tensorflow,ppwwyyxx/tensorflow,yongtang/tensorflow,petewarden/tensorflow,paolodedios/tensorflow,sarvex/tensorflow,frreiss/tensorflow-fred,alsrgv/tensorflow,DavidNorman/tensorflow,Intel-tensorflow/tensorflow,arborh/tensorflow,DavidNorman/tensorflow,xzturn/tensorflow,yongtang/tensorflow,alsrgv/tensorflow,jendap/tensorflow,DavidNorman/tensorflow,adit-chandra/tensorflow,ageron/tensorflow,ageron/tensorflow,ghchinoy/tensorflow,arborh/tensorflow,ghchinoy/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,Intel-tensorflow/tensorflow,adit-chandra/tensorflow,jhseu/tensorflow,ageron/tensorflow,davidzchen/tensorflow,jendap/tensorflow,chemelnucfin/tensorflow,frreiss/tensorflow-fred,adit-chandra/tensorflow,Intel-Corporation/tensorflow,Intel-Corporation/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,tensorflow/tensorflow-pywrap_saved_model,ppwwyyxx/tensorflow,chemelnucfin/tensorflow,annarev/tensorflow,frreiss/tensorflow-fred,tensorflow/tensorflow-pywrap_tf_optimizer,gautam1858/tensorflow,chemelnucfin/tensorflow,DavidNorman/tensorflow,hfp/tensorflow-xsmm,sarvex/tensorflow,paolodedios/tensorflow,gautam1858/tensorflow,paolodedios/tensorflow,Intel-tensorflow/tensorflow,davidzchen/tensorflow,frreiss/tensorflow-fred,alsrgv/tensorflow,alsrgv/tensorflow,arborh/tensorflow,ghchinoy/tensorflow,jendap/tensorflow,frreiss/tensorflow-fred,Intel-tensorflow/tensorflow,freedomtan/tensorflow,Intel-tensorflow/tensorflow,tensorflow/tensorflow-pywrap_saved_model,kevin-coder/tensorflow-fork,xzturn/tensorflow,jbedorf/tensorflow,davidzchen/tensorflow,arborh/tensorflow,jbedorf/tensorflow,gunan/tensorflow,alsrgv/tensorflow,hfp/tensorflow-xsmm,xzturn/tensorflow,jendap/tensorflow,hfp/tensorflow-xsmm,theflofly/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,alsrgv/tensorflow,gautam1858/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,aam-at/tensorflow,aldian/tensorflow,renyi533/tensorflow,ageron/tensorflow,DavidNorman/tensorflow,gunan/tensorflow,yongtang/tensorflow,jhseu/tensorflow,arborh/tensorflow,alsrgv/tensorflow,tensorflow/tensorflow-pywrap_saved_model,davidzchen/tensorflow,gautam1858/tensorflow,jbedorf/tensorflow,hfp/tensorflow-xsmm,hfp/tensorflow-xsmm,tensorflow/tensorflow,adit-chandra/tensorflow,frreiss/tensorflow-fred,ghchinoy/tensorflow,ppwwyyxx/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,adit-chandra/tensorflow,ghchinoy/tensorflow,kevin-coder/tensorflow-fork,sarvex/tensorflow,tensorflow/tensorflow,chemelnucfin/tensorflow,cxxgtxy/tensorflow,ghchinoy/tensorflow,Intel-Corporation/tensorflow,frreiss/tensorflow-fred,theflofly/tensorflow,xzturn/tensorflow,tensorflow/tensorflow-pywrap_saved_model,cxxgtxy/tensorflow,Intel-tensorflow/tensorflow,kevin-coder/tensorflow-fork,apark263/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,jbedorf/tensorflow,paolodedios/tensorflow,freedomtan/tensorflow,aldian/tensorflow,ghchinoy/tensorflow,apark263/tensorflow,aldian/tensorflow,renyi533/tensorflow,aam-at/tensorflow,tensorflow/tensorflow,gautam1858/tensorflow,tensorflow/tensorflow,Intel-Corporation/tensorflow,chemelnucfin/tensorflow,jbedorf/tensorflow,gunan/tensorflow,gautam1858/tensorflow,petewarden/tensorflow,freedomtan/tensorflow,tensorflow/tensorflow-pywrap_saved_model,ageron/tensorflow,chemelnucfin/tensorflow,renyi533/tensorflow,karllessard/tensorflow,annarev/tensorflow,tensorflow/tensorflow-pywrap_saved_model,jbedorf/tensorflow,aam-at/tensorflow,petewarden/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,davidzchen/tensorflow,paolodedios/tensorflow,frreiss/tensorflow-fred,jbedorf/tensorflow,theflofly/tensorflow,jendap/tensorflow,petewarden/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,hfp/tensorflow-xsmm,freedomtan/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,xzturn/tensorflow,arborh/tensorflow,jhseu/tensorflow,kevin-coder/tensorflow-fork,chemelnucfin/tensorflow,xzturn/tensorflow,jendap/tensorflow,jhseu/tensorflow,davidzchen/tensorflow,jhseu/tensorflow,hfp/tensorflow-xsmm,jendap/tensorflow,Intel-tensorflow/tensorflow,jendap/tensorflow,frreiss/tensorflow-fred,renyi533/tensorflow,cxxgtxy/tensorflow,gunan/tensorflow,sarvex/tensorflow,gunan/tensorflow,petewarden/tensorflow,freedomtan/tensorflow,ppwwyyxx/tensorflow,aam-at/tensorflow,hfp/tensorflow-xsmm,kevin-coder/tensorflow-fork,apark263/tensorflow,jhseu/tensorflow,davidzchen/tensorflow,jhseu/tensorflow,aldian/tensorflow,gunan/tensorflow,ppwwyyxx/tensorflow,tensorflow/tensorflow,jbedorf/tensorflow,jhseu/tensorflow,alsrgv/tensorflow,adit-chandra/tensorflow,karllessard/tensorflow,gautam1858/tensorflow,adit-chandra/tensorflow,petewarden/tensorflow,gunan/tensorflow,renyi533/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,aam-at/tensorflow,arborh/tensorflow,adit-chandra/tensorflow,kevin-coder/tensorflow-fork,jendap/tensorflow,xzturn/tensorflow,jbedorf/tensorflow,sarvex/tensorflow,gunan/tensorflow,karllessard/tensorflow,theflofly/tensorflow,ppwwyyxx/tensorflow,ghchinoy/tensorflow,aam-at/tensorflow,aam-at/tensorflow,petewarden/tensorflow,kevin-coder/tensorflow-fork,petewarden/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,alsrgv/tensorflow,aam-at/tensorflow,renyi533/tensorflow,apark263/tensorflow,ghchinoy/tensorflow,arborh/tensorflow,gunan/tensorflow,karllessard/tensorflow,freedomtan/tensorflow,yongtang/tensorflow,hfp/tensorflow-xsmm,cxxgtxy/tensorflow,sarvex/tensorflow,Intel-tensorflow/tensorflow,tensorflow/tensorflow,karllessard/tensorflow,davidzchen/tensorflow,Intel-tensorflow/tensorflow,gautam1858/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,theflofly/tensorflow,annarev/tensorflow,Intel-tensorflow/tensorflow,freedomtan/tensorflow,renyi533/tensorflow,DavidNorman/tensorflow,chemelnucfin/tensorflow,cxxgtxy/tensorflow,ghchinoy/tensorflow,apark263/tensorflow,karllessard/tensorflow,yongtang/tensorflow,apark263/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,ppwwyyxx/tensorflow,ageron/tensorflow,davidzchen/tensorflow