[XFS] Propagate xfs_trans_reserve() errors.

xfs_trans_reserve() reports errors that should not be ignored. For
example, a shutdown filesystem will report errors through
xfs_trans_reserve() to prevent further changes from being attempted on a
damaged filesystem. Catch and propagate all error conditions from
xfs_trans_reserve().

SGI-PV: 980084
SGI-Modid: xfs-linux-melb:xfs-kern:30794a

Signed-off-by: David Chinner <dgc@sgi.com>
Signed-off-by: Niv Sardi <xaiki@sgi.com>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>