Enumeration type documentation comments are not checked, as
demonstrated by test doc-bad-enum-member.  This is because we neglect
to call self.doc.check() for enumeration types.  Messed up in
816a57cd "qapi: Fix detection of bogus member documentation".  Fix
it.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20191024110237.30963-10-armbru@redhat.com>