xfs: avoid setting XFS_ILOG_CORE if i_version doesn't need incrementing

If XFS_ILOG_CORE is already set then go ahead and increment it.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Acked-by: Darrick J. Wong <darrick.wong@oracle.com>
Acked-by: Dave Chinner <dchinner@redhat.com>