qapi/yank: Clean up documentaion of yank

The command's doc comment describes the argument, but it's not marked
up as such.  Easy enough to fix.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-ID: <20240205074709.3613229-11-armbru@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
2 files changed