staging: r8188eu: fix unused variable warnings in core/rtw_ieee80211.c

Remove an unused variable and a set but unused variable within
core/rtw_ieee80211.c to fix a kernel test robot warning.

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Phillip Potter <phil@philpotter.co.uk>
Link: https://lore.kernel.org/r/20210806004034.82233-11-phil@philpotter.co.uk


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