NFSD: Use correct reply size calculating function

ALLOCATE/DEALLOCATE only reply one status value to client,
so, using nfsd4_only_status_rsize for reply size calculating.

Signed-off-by: Kinglong Mee <kinglongmee@gmail.com>
Reviewed-by: Anna Schumaker <Anna.Schumaker@netapp.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>