p54: Fix compile warning

If any of the p54-based drivers are built with CONFIG_P54_LEDS not
defined, the following warning is generated:

  CC [M]  drivers/net/wireless/p54/main.o
drivers/net/wireless/p54/main.c: In function ‘p54_register_common’:
drivers/net/wireless/p54/main.c:614:21: warning: unused variable ‘priv’
Signed-off-by: NLarry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

drivers/net/wireless/p54/main.c

@@ -611,7 +611,7 @@ EXPORT_SYMBOL_GPL(p54_init_common);
 
 int p54_register_common(struct ieee80211_hw *dev, struct device *pdev)
 {
-	struct p54_common *priv = dev->priv;
+	struct p54_common __maybe_unused *priv = dev->priv;
 	int err;
 
 	err = ieee80211_register_hw(dev);