gpg: Re-add the revocation reason to the sigclass in a "rev" record.

* g10/import.c (get_revocation_reason): Fix setting of r_reason.

Note that gpgme has not yet support for parsing the revocation reason.
Due to the split of gpgme it was not tested with gpgmeqt which has its
own parser in its regression tests which kicked it when building
debian packages.

• GnuPG-bug-id: T7083
• Fixes-commit: 3f825b044b2f1db8773f27a96034c925177fe9f0