usb: function_eem: fix eem_read_cb
usb: function_eem: fix eem_read_cb

This patch prevents eem_read_cb from trying to allocate a lot of memory.

It may happen that EEM payload size is zero, the eem_read_cb then tries
to allocate a buffer which is 0xfffc bytes large and luckily blocks.

Signed-off-by: Johann Fischer <b39b26e1812eb092eb217277792f3735321fa456@phytec.de>

nashif/zephyr,GiulianoFranchetto/zephyr,GiulianoFranchetto/zephyr,nashif/zephyr,mbolivar/zephyr,finikorg/zephyr,zephyriot/zephyr,explora26/zephyr,punitvara/zephyr,galak/zephyr,punitvara/zephyr,nashif/zephyr,ldts/zephyr,zephyriot/zephyr,explora26/zephyr,nashif/zephyr,galak/zephyr,ldts/zephyr,finikorg/zephyr,galak/zephyr,galak/zephyr,Vudentz/zephyr,finikorg/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,mbolivar/zephyr,ldts/zephyr,explora26/zephyr,zephyrproject-rtos/zephyr,mbolivar/zephyr,Vudentz/zephyr,kraj/zephyr,mbolivar/zephyr,GiulianoFranchetto/zephyr,zephyriot/zephyr,finikorg/zephyr,Vudentz/zephyr,Vudentz/zephyr,punitvara/zephyr,ldts/zephyr,zephyrproject-rtos/zephyr,kraj/zephyr,punitvara/zephyr,galak/zephyr,GiulianoFranchetto/zephyr,finikorg/zephyr,ldts/zephyr,mbolivar/zephyr,kraj/zephyr,zephyriot/zephyr,explora26/zephyr,kraj/zephyr,zephyrproject-rtos/zephyr,explora26/zephyr,punitvara/zephyr,kraj/zephyr,GiulianoFranchetto/zephyr,zephyriot/zephyr,Vudentz/zephyr