xfs: remove unused tp arg from xfs_bmap_last_offset() and callers

remove unused transaction pointer from various
callchains leading to xfs_bmap_last_offset().

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>