xfs: xfs_swap_extent_flush can be static

Fix sparse warning introduced by commit 4ef897a ("xfs: flush both
inodes in xfs_swap_extents").

Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

fs/xfs/xfs_bmap_util.c

@@ -1618,7 +1618,7 @@ xfs_swap_extents_check_format(
 	return 0;
 }
 
-int
+static int
 xfs_swap_extent_flush(
 	struct xfs_inode	*ip)
 {