qapi: Fix misspelled section tags in doc comments

Section tags are case sensitive and end with a colon.  Screwing up
either gets them interpreted as ordinary paragraph.  Fix a few.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20230425064223.820979-15-armbru@redhat.com>