XLOG_STATE_DO_CALLBACK is only entered through XLOG_STATE_DONE_SYNC
and just used in a single debug check. Remove the flag and thus
simplify the calling conventions for xlog_state_do_callback and
xlog_state_iodone_process_iclog.
Signed-off-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com> Reviewed-by: Brian Foster <bfoster@redhat.com>