xfs: fix a missing unlock on error in xfs_fs_map_blocks

We also need to drop the iolock when invalidate_inode_pages2 fails, not
only on all other error or successful cases.

Fixes: 52785112 ("xfs: implement pNFS export operations")
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

fs/xfs/xfs_pnfs.c

@@ -134,7 +134,7 @@ xfs_fs_map_blocks(
 		goto out_unlock;
 	error = invalidate_inode_pages2(inode->i_mapping);
 	if (WARN_ON_ONCE(error))
-		return error;
+		goto out_unlock;
 
 	end_fsb = XFS_B_TO_FSB(mp, (xfs_ufsize_t)offset + length);
 	offset_fsb = XFS_B_TO_FSBT(mp, offset);