dm cache: add missing cache device name to DMERR in set_cache_mode()

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
diff --git a/drivers/md/dm-cache-target.c b/drivers/md/dm-cache-target.c
index 59b2c50..e04c61e 100644
--- a/drivers/md/dm-cache-target.c
+++ b/drivers/md/dm-cache-target.c
@@ -989,7 +989,8 @@
 	enum cache_metadata_mode old_mode = get_cache_mode(cache);
 
 	if (dm_cache_metadata_needs_check(cache->cmd, &needs_check)) {
-		DMERR("unable to read needs_check flag, setting failure mode");
+		DMERR("%s: unable to read needs_check flag, setting failure mode.",
+		      cache_device_name(cache));
 		new_mode = CM_FAIL;
 	}