clients/simple-dmabuf-egl: do not block until rendering completes

glFinish() blocks until all commands have finished. This is
unnecessary: we can use glFlush() and rely on implicit sync
instead.

Signed-off-by: Simon Ser <contact@emersion.fr>

clients/simple-dmabuf-egl.c

@@ -1010,7 +1010,7 @@ redraw(void *data, struct wl_callback *callback, uint32_t time)
 		zwp_linux_buffer_release_v1_add_listener(
 			buffer->buffer_release, &buffer_release_listener, buffer);
 	} else {
-		glFinish();
+		glFlush();
 	}
 
 	wl_surface_attach(window->surface, buffer->buffer, 0, 0);