Fix btrfs_fill_super to return -EINVAL when no FS found

Signed-off-by: Chris Mason <chris.mason@oracle.com>
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index d8fce32..169be0f 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -237,7 +237,7 @@
 	if (strncmp((char *)(&disk_super->magic), BTRFS_MAGIC,
 	    sizeof(disk_super->magic))) {
 		printk("no btrfs found on %s\n", path);
-		ret = -ENOENT;
+		ret = -EINVAL;
 		goto error_brelse;
 	}
 	devid = le64_to_cpu(disk_super->dev_item.devid);