compositor-drm: Fix invalid usage of udev ressources

The reference returned by udev_list_entry_get_name is
only valid until udev_enumerate_unref is called.
Call unref after the last usage of such.

compositor/compositor-drm.c

@@ -826,8 +826,6 @@ drm_compositor_create(struct wl_display *display,
 		udev_device_unref(device);
 	}
 
-	udev_enumerate_unref(e);
-
 	if (drm_device == NULL) {
 		fprintf(stderr, "no drm device found\n");
 		return NULL;
@@ -858,6 +856,9 @@ drm_compositor_create(struct wl_display *display,
 		return NULL;
 	}
 
+	udev_enumerate_unref(e);
+	path = NULL;
+
 	evdev_input_add_devices(&ec->base, ec->udev, seat);
 
 	loop = wl_display_get_event_loop(ec->base.wl_display);