backend-drm: ignore heads from other devices

The compositor lists the heads from all devices, but we must only disable the
connectors that belong to the current device. Therefore, other heads must be
ignored.

Signed-off-by: Michael Tretter <m.tretter@pengutronix.de>

libweston/backend-drm/kms.c

@@ -1112,6 +1112,8 @@ drm_pending_state_apply_atomic(struct drm_pending_state *pending_state,
 
 			head = to_drm_head(head_base);
 			connector_id = head->connector.connector_id;
+			if (head->connector.device != device)
+				continue;
 
 			drm_debug(b, "\t\t[atomic] disabling inactive head %s\n",
 				  head_base->name);