xfs: fix inode pincount check in fsync

We need to hold the ilock to check the inode pincount safely.  While
we're at it also remove the check for ip->i_itemp->ili_last_lsn, a
pinned inode always has it set.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <david@fromorbit.com>
Signed-off-by: Alex Elder <aelder@sgi.com>