qapi: Fix mangled "Returns" sections in documentation

qapi: Fix mangled "Returns" sections in documentation

Commit e050e426782e (qapi: Use explicit bulleted lists) added list
markup to correct bad rendering:

    A JSON block comment like this:
         Returns: nothing on success
                  If @node is not a valid block device, DeviceNotFound
                  If @name is not found, GenericError with an explanation

    renders like this:

         Returns: nothing on success If node is not a valid block device,
         DeviceNotFound If name is not found, GenericError with an explanation

    because whitespace is not significant.

    Use an actual bulleted list, so that the formatting is correct.

It missed a few instances.  Commit a937b6aa739 (qapi: Reformat doc
comments to conform to current conventions) then reflowed them.

Revert the reflowing, and add list markup.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-ID: <20240120095327.666239-6-armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>