qapi: Add spaces after symbol declaration for consistency

Several QGA definitions omit a blank line after the symbol
declaration. This works OK currently, but it's the only place where we
do this. Adjust it for consistency.

Future commits may wind up enforcing this formatting.

Signed-off-by: John Snow <jsnow@redhat.com>

Message-Id: <20210930205716.1148693-5-jsnow@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>