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>
diff --git a/drivers/net/wireless/b43legacy/main.c b/drivers/net/wireless/b43legacy/main.c
index c1324e3..fb996c2 100644
--- a/drivers/net/wireless/b43legacy/main.c
+++ b/drivers/net/wireless/b43legacy/main.c
@@ -2465,7 +2465,7 @@
 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;