[XFS] Never call mark_inode_dirty_sync() directly

Once the Linux inode and the XFS inode are combined, we cannot rely on
just check if the linux inode exists as a method of determining if it is
valid or not. Hence we should always call xfs_mark_inode_dirty_sync()
instead as it does the correct checks to determine if the liinux inode is
in a valid state or not.

SGI-PV: 988141

SGI-Modid: xfs-linux-melb:xfs-kern:32318a

Signed-off-by: David Chinner <david@fromorbit.com>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>
Signed-off-by: Christoph Hellwig <hch@infradead.org>