(sunxi) Wire sunxi_get_refresh_rate into the poke

 interface

The function was added in c4f8185 ("Add some fbdev refresh rate polls.
Also Xv.") but the get_refresh_rate slot in sunxi_poke_interface was
never updated, so the poll never fired.

Author: LibretroAdmin

gfx/drivers/sunxi_gfx.c

@@ -937,7 +937,7 @@ static const video_poke_interface_t sunxi_poke_interface = {
    NULL, /* load_texture */
    NULL, /* unload_texture */
    NULL, /* set_video_mode */
-   NULL, /* get_refresh_rate */
+   sunxi_get_refresh_rate,
    NULL, /* set_filtering */
    NULL, /* get_video_output_size */
    NULL, /* get_video_output_prev */