vrend: fix next ubo id when there is no update

When there is no change to UBOs of a shader stage, we still need to
increment next_ubo_id to match bind_ubo_locs.  This was regressed by
commit 2192c92 (renderer: only update dirty constbufs).

Signed-off-by: Chia-I Wu <olvaffe@gmail.com>
Reviewed-by: Gert Wollny <gert.wollny@collabora.com>

src/vrend_renderer.c

@@ -3862,7 +3862,7 @@ static int vrend_draw_bind_ubo_shader(struct vrend_context *ctx,
    update = dirty & ctx->sub->const_bufs_used_mask[shader_type];
 
    if (!update)
-      return next_ubo_id;
+      return next_ubo_id + util_bitcount(mask);
 
    while (mask) {
       /* The const_bufs_used_mask stores the gallium uniform buffer indices */