staging: rtl8723bs: Remove comparisons to NULL in conditionals

Remove most comparisons to NULL in conditionals in
drivers/staging/rtl8723bs/core/rtw_mlme.c
Issues reported by checkpatch.pl as:
CHECK: Comparison to NULL could be written

Signed-off-by: Wambui Karuga <wambui.karugax@gmail.com>
Link: https://lore.kernel.org/r/f4752d3a49e02193ed7b47a353e18e56d94b5a68.1570712632.git.wambui.karugax@gmail.com


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