x25: remove redundant pointer dev

Pointer dev is being assigned a value that is never used, the assignment
and the variable are redundant and can be removed. Also replace null check
with the preferred !ptr idiom.

Cleans up clang scan warning:
net/x25/x25_proc.c:94:26: warning: Although the value stored to 'dev' is
used in the enclosing expression, the value is never actually read
from 'dev' [deadcode.DeadStores]
Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Link: https://lore.kernel.org/r/20220508214500.60446-1-colin.i.king@gmail.comSigned-off-by: Paolo Abeni <pabeni@redhat.com>

net/x25/x25_proc.c

@@ -79,7 +79,6 @@ static int x25_seq_socket_show(struct seq_file *seq, void *v)
 {
 	struct sock *s;
 	struct x25_sock *x25;
-	struct net_device *dev;
 	const char *devname;
 
 	if (v == SEQ_START_TOKEN) {
@@ -91,7 +90,7 @@ static int x25_seq_socket_show(struct seq_file *seq, void *v)
 	s = sk_entry(v);
 	x25 = x25_sk(s);
 
-	if (!x25->neighbour || (dev = x25->neighbour->dev) == NULL)
+	if (!x25->neighbour || !x25->neighbour->dev)
 		devname = "???";
 	else
 		devname = x25->neighbour->dev->name;