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>
diff --git a/drivers/isdn/i4l/isdn_bsdcomp.c b/drivers/isdn/i4l/isdn_bsdcomp.c
index c59e8d2..8837ac5 100644
--- a/drivers/isdn/i4l/isdn_bsdcomp.c
+++ b/drivers/isdn/i4l/isdn_bsdcomp.c
@@ -612,7 +612,7 @@
 		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;