staging: rtl8723au: core: add consistent spacing around '-'

This patch fixes checkpatch.pl error in file rtw_ap.c
ERROR: need consistent spacing around '-' (ctx:WxV)

Signed-off-by: Tapasweni Pathak <tapaswenipathak@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>