cifs: don't override the uid/gid in getattr when cifsacl is enabled

If we're using cifsacl, then we don't want to override the uid/gid with
the current uid/gid, since that would prevent you from being able to
upcall for this info.

Reviewed-by: Shirish Pargaonkar <shirishpargaonkar@gmail.com>
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <smfrench@gmail.com>