staging: r8188eu: remove set but unused variable from rtl8188e_Add_RateATid

staging: r8188eu: remove set but unused variable from rtl8188e_Add_RateATid

Remove set but unused variable init_rate from the rtl8188e_Add_RateATid
function in hal/rtl8188eu_cmd.c, as this fixes a kernel test robot
warning. Removing the call to get_highest_rate_idx has no side effects
here so is safe.

Reported-by: kernel test robot <lkp@intel.com>
Acked-by: Michael Straube <straube.linux@gmail.com>
Signed-off-by: Phillip Potter <phil@philpotter.co.uk>
Link: https://lore.kernel.org/r/20210816234459.132239-2-phil@philpotter.co.uk
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>