[XFS] Catch errors from xfs_imap().

Catch errors from xfs_imap() in log recovery when we might be trying to
map an invalid inode number due to a corrupted log.

SGI-PV: 980084
SGI-Modid: xfs-linux-melb:xfs-kern:30829a

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