tg3: sparse cleanup

Fix the following sparse warning :

drivers/net/tg3.c:4025:3: warning: context imbalance in 'tg3_restart_hw' 
- unexpected unlock

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/tg3.c b/drivers/net/tg3.c
index bc4c62b..e3f74c9 100644
--- a/drivers/net/tg3.c
+++ b/drivers/net/tg3.c
@@ -4017,6 +4017,8 @@
  * Invoked with tp->lock held.
  */
 static int tg3_restart_hw(struct tg3 *tp, int reset_phy)
+	__releases(tp->lock)
+	__acquires(tp->lock)
 {
 	int err;