crypto: ensure qapi/crypto.json is listed in qapi-modules

The rebuild of qapi-types.c/h is not correctly triggered
when qapi/crypto.json is changed because it was missing
from the list of files in the qapi-modules variable.

Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>