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/disk-io.c b/fs/btrfs/disk-io.c
index 709e33d..5547607 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -728,9 +728,8 @@
 	struct btrfs_root *dev_root = kmalloc(sizeof(struct btrfs_root),
 					      GFP_NOFS);
 	int ret;
-	int err = -EIO;
+	int err = -EINVAL;
 	struct btrfs_super_block *disk_super;
-
 	if (!extent_root || !tree_root || !fs_info) {
 		err = -ENOMEM;
 		goto fail;