staging: rtl8188eu: cleanup comparsion to NULL in usb_halinit.c

Use if(!x) instead of if(x == NULL).
Reported by checkpatch.
Signed-off-by: Michael Straube <straube.linux@gmail.com>
Acked-by: Larry Finger <Larry.Finger@lwfinger.net>
Link: https://lore.kernel.org/r/20190726180448.2290-6-straube.linux@gmail.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/rtl8188eu/hal/usb_halinit.c

@@ -1889,7 +1889,7 @@ void UpdateHalRAMask8188EUsb(struct adapter *adapt, u32 mac_id, u8 rssi_level)
 	if (mac_id >= NUM_STA) /* CAM_SIZE */
 		return;
 	psta = pmlmeinfo->FW_sta_info[mac_id].psta;
-	if (psta == NULL)
+	if (!psta)
 		return;
 	switch (mac_id) {
 	case 0:/*  for infra mode */