video_driver: guard crt_switch_display_server_lost with HAVE_VIDEOCORE

crt_switch_display_server_lost() (video_crt_switch.c) is defined
inside #if !defined(HAVE_VIDEOCORE) - VideoCore keeps its own
tvservice path and doesn't use the modeline ops table. The call
added in 94d23651 (\"crt: rebind the modeline ops when the display
server is rebuilt under a live engine\") only checked HAVE_MODELINE,
so any build with both HAVE_MODELINE and HAVE_VIDEOCORE (e.g. Lakka
RPiZero/RPiZero2 with the bcm2835-driver GLES stack) fails to link:

  video_driver.c:(.text+0x20e8): undefined reference to
  \`crt_switch_display_server_lost'

Add the same !defined(HAVE_VIDEOCORE) guard at the call site.

gfx/video_driver.c

@@ -1728,7 +1728,7 @@ void video_display_server_destroy(void)
    if (current_display_server && (current_display_server != &dispserv_null))
       if (video_st->current_display_server_data)
       {
-#if defined(HAVE_MODELINE)
+#if defined(HAVE_MODELINE) && !defined(HAVE_VIDEOCORE)
          crt_switch_display_server_lost(&video_st->crt_switch_st,
                video_st->current_display_server_data);
 #endif