onscreen/native: Associate the kms_crtc with EGL_DEVICE updates

Although we track updates for EGL_DEVICE, they are often empty because
the primary plane has a custom page flip method. That means there's
no CRTC latched yet, but we do know exactly which CRTC is associated
with the flip. Set it so the update can still be processed.

Fixes: 27ed069766 ("kms/impl-device: Add deadline based KMS commit scheduling")
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3939>

src/backends/native/meta-onscreen-native.c

@@ -583,6 +583,7 @@ meta_onscreen_native_flip_crtc (CoglOnscreen           *onscreen,
       break;
 #ifdef HAVE_EGL_DEVICE
     case META_RENDERER_NATIVE_MODE_EGL_DEVICE:
+      meta_kms_update_set_flushing (kms_update, kms_crtc);
       meta_kms_update_set_custom_page_flip (kms_update,
                                             custom_egl_stream_page_flip,
                                             onscreen_native);