NFS: return -ENOKEY when the upcall fails to map the name

commit 12dfd080556124088ed61a292184947711b46cbe upstream.

This allows the normal error-paths to handle the error, rather than
making a special call to complete_request_key() just for this instance.

Signed-off-by: Bryan Schumaker <bjschuma@netapp.com>
Tested-by: William Dauchy <wdauchy@gmail.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>