staging: rtl8192e: Rename variables rateIndex and rateBitmap to avoid CamelCase

Rename variables
* rateIndex to rate_index
* rateBitmap to rate_bitmap
to avoid CamelCase which is not accepted by checkpatch.pl .

Signed-off-by: Yogesh Hegde <yogi.kernel@gmail.com>
Link: https://lore.kernel.org/r/20221030133204.GA416592@zephyrus


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>