ovl: fix freeze protection bypass in ovl_clone_file_range()

Tested by doing clone on overlayfs while upper xfs+reflink is frozen:

  xfs_io -f /ovl/y
                             fsfreeze -f /xfs
  xfs_io> reflink /ovl/x

Before the fix xfs_io enters xfs_reflink_remap_range() and blocks
in xfs_trans_alloc(). After the fix, xfs_io blocks outside xfs code
in ovl_clone_file_range().

Fixes: 8ede205541 ("ovl: add reflink/copyfile/dedup support")
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/overlayfs/file.c

@@ -461,7 +461,7 @@ static ssize_t ovl_copyfile(struct file *file_in, loff_t pos_in,
 		break;
 
 	case OVL_CLONE:
-		ret = vfs_clone_file_range(real_in.file, pos_in,
+		ret = do_clone_file_range(real_in.file, pos_in,
 					   real_out.file, pos_out, len);
 		break;