ext4: Reduce "mounted" log from INFO to DEBUG

This is a MPI specific adjustment.

We currently do a lot of ext4 mounts, because we mount inidivdual ext4
filesystems as a tmpdir for each job in the cluster. So we have a lot of
these messages in the logs:

    [2748664.200013] EXT4-fs (loop0): mounted filesystem without journal. Opts: (null)
    [2748709.929436] EXT4-fs (loop1): mounted filesystem without journal. Opts: (null)
    [2748732.185899] EXT4-fs (loop0): mounted filesystem without journal. Opts: (null)

Avoid log spam by reducing the log level of the message from INFO to
DEBUG.

fs/ext4/super.c

@@ -5108,7 +5108,7 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 	}
 
 	if (___ratelimit(&ext4_mount_msg_ratelimit, "EXT4-fs mount"))
-		ext4_msg(sb, KERN_INFO, "mounted filesystem with%s. "
+		ext4_msg(sb, KERN_DEBUG, "mounted filesystem with%s. "
 			 "Opts: %.*s%s%s", descr,
 			 (int) sizeof(sbi->s_es->s_mount_opts),
 			 sbi->s_es->s_mount_opts,