wireless: ERR_PTR vs null

iwm_wdev_alloc() returns an ERR_PTR on failure and not null.  It also
prints its own dev_err() message so I removed that as well.

Compile tested only.  Sorry.
Found by smatch (http://repo.or.cz/w/smatch.git).
Signed-off-by: Dan Carpenter <error27@gmail.com>
Acked-by: Zhu Yi <yi.zhu@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/iwmc3200wifi/netdev.c

@@ -106,10 +106,8 @@ void *iwm_if_alloc(int sizeof_bus, struct device *dev,
 	int ret = 0;
 
 	wdev = iwm_wdev_alloc(sizeof_bus, dev);
-	if (!wdev) {
-		dev_err(dev, "no memory for wireless device instance\n");
-		return ERR_PTR(-ENOMEM);
-	}
+	if (IS_ERR(wdev))
+		return wdev;
 
 	iwm = wdev_to_iwm(wdev);
 	iwm->bus_ops = if_ops;