staging: rtl8192u: Replace explicit NULL comparison

Replace explicit NULL comparison with ! operator to
simplify code.

Found with Coccinelle script:
@@
expression ptr;
position p;
statement s0, s1;
@@

ptr@p =
\(kmalloc\|devm_kzalloc\|kmalloc_array\|devm_ioremap\|usb_alloc_urb\|
alloc_netdev\|dev_alloc_skb\)(...)
... when != ptr

if (
(
+ !
ptr
- == NULL
)
) s0 else s1

Signed-off-by: Gargi Sharma <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/staging/rtl8192u/ieee80211/rtl819x_BAProc.c

···
 		return NULL;
 	}
 	skb = dev_alloc_skb(len + sizeof( struct rtl_80211_hdr_3addr)); //need to add something others? FIXME
-	if (skb == NULL) {
+	if (!skb) {
 		IEEE80211_DEBUG(IEEE80211_DL_ERR, "can't alloc skb for ADDBA_REQ\n");
 		return NULL;
 	}
···
 	DelbaParamSet.field.TID	= pBA->BaParamSet.field.TID;
 
 	skb = dev_alloc_skb(len + sizeof( struct rtl_80211_hdr_3addr)); //need to add something others? FIXME
-	if (skb == NULL) {
+	if (!skb) {
 		IEEE80211_DEBUG(IEEE80211_DL_ERR, "can't alloc skb for ADDBA_REQ\n");
 		return NULL;
 	}