mISDN: prevent possible NULL pointer dereference

A return value of the bchannel_get_rxbuf() function is compared with the
positive ENOMEM value instead of the negative -ENOMEM value to detect a
memory allocation problem. Thus, after a possible memory allocation
failure the bc->bch.rx_skb will be NULL which will lead to a NULL
pointer dereference.

Signed-off-by: Anton Protopopov <a.s.protopopov@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/isdn/hardware/mISDN/netjet.c b/drivers/isdn/hardware/mISDN/netjet.c
index 8e29447..afde4ed 100644
--- a/drivers/isdn/hardware/mISDN/netjet.c
+++ b/drivers/isdn/hardware/mISDN/netjet.c
@@ -392,7 +392,7 @@
 	}
 	stat = bchannel_get_rxbuf(&bc->bch, cnt);
 	/* only transparent use the count here, HDLC overun is detected later */
-	if (stat == ENOMEM) {
+	if (stat == -ENOMEM) {
 		pr_warning("%s.B%d: No memory for %d bytes\n",
 			   card->name, bc->bch.nr, cnt);
 		return;