turnip: Make sure bandwidth config per pixel starts from 0.

We'd keep incrementing the costs in a cmd buffer's dynamic_pass on each
BeginRendering.  This fixes the main renderpass of aztec ruins on zink to
use gmem, taking fps from ~8 to ~10.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/18352>

src/freedreno/vulkan/tu_pass.c

@@ -639,6 +639,9 @@ tu_render_pass_gmem_config(struct tu_render_pass *pass,
 static void
 tu_render_pass_bandwidth_config(struct tu_render_pass *pass)
 {
+   pass->gmem_bandwidth_per_pixel = 0;
+   pass->sysmem_bandwidth_per_pixel = 0;
+
    for (uint32_t i = 0; i < pass->attachment_count; i++) {
       const struct tu_render_pass_attachment *att = &pass->attachments[i];