staging: r8188eu: rename variable within rtl8188e_Add_RateATid

Rename 'shortGIrate' within the rtl8188e_Add_RateATid function to
'short_gi_rate', to comply with kernel camel case style rules.

Signed-off-by: Phillip Potter <phil@philpotter.co.uk>
Link: https://lore.kernel.org/r/20210818180831.67581-1-phil@philpotter.co.uk


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