Get rid of xfs_buf_log_item_t typedef

Take advantage of the rework on xfs_buf log items list, to get rid of
ths typedef for xfs_buf_log_item.

This patch also fix some indentation alignment issues found along the way.

Signed-off-by: Carlos Maiolino <cmaiolino@redhat.com>
Reviewed-by: Bill O'Donnell <billodo@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>