[XFS] Add xfs_map_buffer helper, use it in a couple of places. 

SGI-PV: 950211
SGI-Modid: xfs-linux-melb:xfs-kern:25312a

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Nathan Scott <nathans@sgi.com>
1 file changed