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>

drivers/staging/rtl8723au/core/rtw_ap.c

@@ -84,7 +84,7 @@ static void update_BCNTIM(struct rtw_adapter *padapter)
 
 		premainder_ie = p+tim_ielen;
 
-		tim_ie_offset = (int)(p -pie);
+		tim_ie_offset = (int)(p - pie);
 
 		remainder_ielen = pnetwork_mlmeext->IELength - tim_ie_offset - tim_ielen;