NFSD: FIDs need to take precedence over UUIDs

When determining the fsid_type in fh_compose(), the setting of the FID
via fsid= export option needs to take precedence over using the UUID
device id.

Signed-off-by: Steve Dickson <steved@redhat.com>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>