be2net: use mutex instead of spin lock for mbox_lock

Since the mbox polling uses the schedule_timeout, the mbox_lock should be
a mutex and not a spin lock.
The commit f25b03a replaced udelay() with schedule_timeout() but didn't
change mbox_lock to semaphore or mutex.

Signed-off-by: Ivan Vecera <ivecera@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/benet/be.h b/drivers/net/benet/be.h
index 4594a28..d64313b 100644
--- a/drivers/net/benet/be.h
+++ b/drivers/net/benet/be.h
@@ -234,7 +234,7 @@
 	u8 __iomem *db;		/* Door Bell */
 	u8 __iomem *pcicfg;	/* PCI config space */
 
-	spinlock_t mbox_lock;	/* For serializing mbox cmds to BE card */
+	struct mutex mbox_lock; /* For serializing mbox cmds to BE card */
 	struct be_dma_mem mbox_mem;
 	/* Mbox mem is adjusted to align to 16 bytes. The allocated addr
 	 * is stored for freeing purpose */