yam: remove redundant null check on dev

yam_open has a redundant null check on null,  it will
never be called with dev == NULL. Remove this redundant check.
This also cleans up a smatch warning:

drivers/net/hamradio/yam.c:869 yam_open() warn: variable
  dereferenced before check 'dev' (see line 867)
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Reviewed-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/hamradio/yam.c

@@ -866,7 +866,7 @@ static int yam_open(struct net_device *dev)
 
 	printk(KERN_INFO "Trying %s at iobase 0x%lx irq %u\n", dev->name, dev->base_addr, dev->irq);
 
-	if (!dev || !yp->bitrate)
+	if (!yp->bitrate)
 		return -ENXIO;
 	if (!dev->base_addr || dev->base_addr > 0x1000 - YAM_EXTENT ||
 		dev->irq < 2 || dev->irq > 15) {