Fix the Efficientnet input normalization issue.
Fix the Efficientnet input normalization issue.

Fix https://github.com/tensorflow/tensorflow/issues/49930

We were incorrectly normalize the input (with wrong variance).

The validation acc after this fix with imagenet is:

b0 0.7699
b1 0.7875
b2 0.7979
b3 0.8141
b4 0.8294

PiperOrigin-RevId: 427329018

keras-team/keras,keras-team/keras