dm mpath: log device name

Make the mapped device structure accessible to hardware handlers so error
messages can include the device name.

Signed-off-by: Edward Goggin <egoggin@emc.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 11a98df..2717a35 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1236,6 +1236,7 @@
 		free_dev(md);
 	}
 }
+EXPORT_SYMBOL_GPL(dm_put);
 
 /*
  * Process the deferred bios