ceph: downgrade warning from mdsmap decode to debug

While the MDS cluster is unstable and changing state the client may get
mdsmap updates that will trigger warnings:

  [144692.478400] ceph: mdsmap_decode got incorrect state(up:standby-replay)
  [144697.489552] ceph: mdsmap_decode got incorrect state(up:standby-replay)
  [144697.489580] ceph: mdsmap_decode got incorrect state(up:standby-replay)

This patch downgrades these warnings to debug, as they may flood the logs
if the cluster is unstable for a while.
Signed-off-by: Luis Henriques <lhenriques@suse.de>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

fs/ceph/mdsmap.c

@@ -243,8 +243,8 @@ struct ceph_mdsmap *ceph_mdsmap_decode(void **p, void *end)
 		}
 
 		if (state <= 0) {
-			pr_warn("mdsmap_decode got incorrect state(%s)\n",
-				ceph_mds_state_name(state));
+			dout("mdsmap_decode got incorrect state(%s)\n",
+			     ceph_mds_state_name(state));
 			continue;
 		}