Bring gears example up to date

Must have gears.
diff --git a/clients/window.h b/clients/window.h
index d7a632e..871e46b 100644
--- a/clients/window.h
+++ b/clients/window.h
@@ -47,6 +47,10 @@
 #ifdef EGL_NO_DISPLAY
 EGLDisplay
 display_get_egl_display(struct display *d);
+
+EGLImageKHR
+display_get_image_for_drm_surface(struct display *display,
+				  cairo_surface_t *surface);
 #endif
 
 cairo_surface_t *