isdn: remove duplicate NULL check

We test both "!skb_out" and "skb_out" here which is duplicative and
causes a static checker warning.  I considered that the intent might
have been to test "skb_in" but that's a valid pointer here.
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/isdn/i4l/isdn_bsdcomp.c

@@ -612,7 +612,7 @@ static int bsd_compress(void *state, struct sk_buff *skb_in, struct sk_buff *skb
 		db->n_bits++;
 
 	/* If output length is too large then this is an incompressible frame. */
-	if (!skb_out || (skb_out && skb_out->len >= skb_in->len)) {
+	if (!skb_out || skb_out->len >= skb_in->len) {
 		++db->incomp_count;
 		db->incomp_bytes += isize;
 		return 0;