anv: fix a cmd_buffer reference in simple shader

In utrace timestamp copy case cmd_buffer is NULL.

Fixes: dbbcd5c32c ("anv: factor out generation kernel dispatch into helper")
Signed-off-by: Tapani Pälli <tapani.palli@intel.com>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/30475>

src/intel/vulkan/genX_simple_shader.c

@@ -110,7 +110,8 @@ genX(emit_simpler_shader_init_fragment)(struct anv_simple_shader *state)
 
    genX(emit_l3_config)(batch, device, state->l3_config);
 
-   state->cmd_buffer->state.current_l3_config = state->l3_config;
+   if (state->cmd_buffer)
+      state->cmd_buffer->state.current_l3_config = state->l3_config;
 
    enum intel_urb_deref_block_size deref_block_size;
    genX(emit_urb_setup)(device, batch, state->l3_config,