[XFS] find_exported_dentry(). XFS does not need to use this symbol as it

is provided by a vector through the superblock export operations when the
filesystem is exported by NFS. The fix is to call that vector instead of
using the exported symbol directly.

SGI-PV: 948858
SGI-Modid: xfs-linux-melb:xfs-kern:25062a

Signed-off-by: David Chinner <dgc@sgi.com>
Signed-off-by: Nathan Scott <nathans@sgi.com>