gallium/draw: Fix intermittent failure to bind new geometry shaders.

If you deleted your old GS and created a new one, then it would
occasionally skip binding the new GS because the token pointers were
equal.  Clear the current token pointer in the machine when we're deleting
its token.

Cc: mesa-stable
Reviewed-by: Dave Airlie <airlied@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/8277>

src/gallium/auxiliary/draw/draw_gs.c

@@ -964,6 +964,9 @@ void draw_delete_geometry_shader(struct draw_context *draw,
    }
 #endif
 
+   if (draw->gs.tgsi.machine && draw->gs.tgsi.machine->Tokens == dgs->state.tokens)
+      draw->gs.tgsi.machine->Tokens = NULL;
+
    for (i = 0; i < TGSI_MAX_VERTEX_STREAMS; i++)
       FREE(dgs->stream[i].primitive_lengths);