d/rules: Disable cloudproviders for downstreams as well

Commit e06fffe5 "Disable cloudproviders" did it strictly for
Apertis, use `--derives-from` to make it apply to downstreams as well.

Signed-off-by: Emanuele Aina <emanuele.aina@collabora.com>

debian/rules

@@ -133,7 +133,7 @@ ifeq ($(shell dpkg-vendor --is Ubuntu && echo yes), yes)
 # Not in main repository
 configure_flags_deb += -Dcloudproviders=disabled
 # libcloudproviders is under LGPL-3
-else ifeq ($(shell dpkg-vendor --is apertis && echo yes), yes)
+else ifeq ($(shell dpkg-vendor --derives-from apertis && echo yes), yes)
 configure_flags_deb += -Dcloudproviders=disabled
 else
 configure_flags_deb += -Dcloudproviders=enabled