conversion.

Since bma.conv is a char and XFS_BMAPI_CONVERT is 0x1000, bma.conv was
always assigned zero. Spotted by the GNU C compiler (SVN version).

SGI-PV: 947312
SGI-Modid: xfs-linux-melb:xfs-kern:26887a
Signed-off-by: NAdrian Bunk <bunk@stusta.de>
Signed-off-by: NNathan Scott <nathans@sgi.com>