b43legacy: fix "‘up_dev’ may be used uninitialized" warning

drivers/net/wireless/b43legacy/main.c: In function ‘b43legacy_op_dev_config’:
drivers/net/wireless/b43legacy/main.c:2468: warning: ‘up_dev’ may be used uninitialized in this function

Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/b43legacy/main.c

@@ -2465,7 +2465,7 @@ static void b43legacy_put_phy_into_reset(struct b43legacy_wldev *dev)
 static int b43legacy_switch_phymode(struct b43legacy_wl *wl,
 				      unsigned int new_mode)
 {
-	struct b43legacy_wldev *up_dev;
+	struct b43legacy_wldev *uninitialized_var(up_dev);
 	struct b43legacy_wldev *down_dev;
 	int err;
 	bool gmode = 0;