aux/trace: avoid deadlock in screen::flush_frontbuffer hook

this hook usually requires mapping a resource, which will trigger a
trace dump internally, which requires locking the output mutex, so
finish the trace dump before calling it

Acked-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/11052>

src/gallium/auxiliary/driver_trace/tr_screen.c

@@ -409,9 +409,9 @@ trace_screen_flush_frontbuffer(struct pipe_screen *_screen,
    trace_dump_arg(ptr, context_private);
    */
 
-   screen->flush_frontbuffer(screen, pipe, resource, level, layer, context_private, sub_box);
-
    trace_dump_call_end();
+
+   screen->flush_frontbuffer(screen, pipe, resource, level, layer, context_private, sub_box);
 }