gallium: fix render to depth texture

src/mesa/state_tracker/st_atom_framebuffer.c

@@ -127,6 +127,11 @@ update_framebuffer_state( struct st_context *st )
    strb = st_renderbuffer(fb->Attachment[BUFFER_DEPTH].Renderbuffer);
    if (strb) {
       strb = st_renderbuffer(strb->Base.Wrapped);
+      if (strb->rtt) {
+         /* rendering to a GL texture, may have to update surface */
+         update_renderbuffer_surface(st, strb);
+      }
+
       assert(strb->surface);
       framebuffer->zsbuf = strb->surface;
    }