[XFS] Fix rounding bug in xfs_free_file_space found by sparse checking.

SGI-PV: 954580
SGI-Modid: xfs-linux-melb:xfs-kern:26551a

Signed-off-by: Nathan Scott <nathans@sgi.com>
Signed-off-by: Tim Shimmin <tes@sgi.com>
1 file changed