python/qemu/qmp/legacy: Replace 'returns-whitelist' with the correct type

'returns-whitelist' has been renamed to 'command-returns-exceptions' in
commit b86df3747848 ("qapi: Rename pragma *-whitelist to *-exceptions").

Message-Id: <20220711095721.61280-1-thuth@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
1 file changed