[RFKILL]: Fix check for correct rfkill allocation

coverity has spotted a bug in rfkill.c (bug id #1627),
in rfkill_allocate() NULL was returns if the kzalloc() works,
and deref the NULL pointer if it fails,
Signed-off-by: NIvo van Doorn <IvDoorn@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/rfkill/rfkill.c

@@ -296,7 +296,7 @@ struct rfkill *rfkill_allocate(struct device *parent, enum rfkill_type type)
 	struct device *dev;
 
 	rfkill = kzalloc(sizeof(struct rfkill), GFP_KERNEL);
-	if (rfkill)
+	if (!rfkill)
 		return NULL;
 
 	mutex_init(&rfkill->mutex);