staging: rtl8723bs: fix issue Comparison to NULL

This patch fixes below issues reported by checkpatch

CHECK: Comparison to NULL could be written "rtw_proc"
CHECK: Comparison to NULL could be written "!rtw_proc"
CHECK: Comparison to NULL could be written "!rtw_proc"

Signed-off-by: Hariprasad Kelam <hariprasad.kelam@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>