[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: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/rfkill/rfkill.c b/net/rfkill/rfkill.c
index a973603..f3986d4 100644
--- a/net/rfkill/rfkill.c
+++ b/net/rfkill/rfkill.c
@@ -296,7 +296,7 @@
 	struct device *dev;
 
 	rfkill = kzalloc(sizeof(struct rfkill), GFP_KERNEL);
-	if (rfkill)
+	if (!rfkill)
 		return NULL;
 
 	mutex_init(&rfkill->mutex);