usbnet: allow type check of devdbg arguments in non-debug build

Improve usbnet's devdbg to always type-check diagnostic arguments,
like dev_dbg (device.h).  This makes no change to the resulting size of
usbnet modules.

This patch also removes an #ifdef DEBUG directive from rndis_wlan so
it's devdbg statements are always type-checked at compile time.
Signed-off-by: Steve Glendinning <steve.glendinning@smsc.com>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/wireless/rndis_wlan.c

@@ -1649,9 +1649,7 @@ static char *rndis_translate_scan(struct net_device *dev,
 				  char *end_buf,
 				  struct ndis_80211_bssid_ex *bssid)
 {
-#ifdef DEBUG
 	struct usbnet *usbdev = netdev_priv(dev);
-#endif
 	u8 *ie;
 	char *current_val;
 	int bssid_len, ie_len, i;

include/linux/usb/usbnet.h

@@ -197,7 +197,9 @@ extern int usbnet_nway_reset(struct net_device *net);
 #define devdbg(usbnet, fmt, arg...) \
 	printk(KERN_DEBUG "%s: " fmt "\n" , (usbnet)->net->name , ## arg)
 #else
-#define devdbg(usbnet, fmt, arg...) do {} while(0)
+#define devdbg(usbnet, fmt, arg...) \
+	({ if (0) printk(KERN_DEBUG "%s: " fmt "\n" , (usbnet)->net->name , \
+		## arg); 0; })
 #endif
 
 #define deverr(usbnet, fmt, arg...) \