mesa/vulkan: use a simpler path for header in trampoline gen

This works better if vk_dispatch_table.h is inside some "genDir",
and not generated "src/vulkan/util" directory.  This is the
case for the AOSP Soong build system.

Reviewed-by: Aaron Ruby <aruby@blackberry.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/26874>

src/vulkan/util/vk_dispatch_trampolines_gen.py

@@ -40,7 +40,7 @@ TEMPLATE_H = Template(COPYRIGHT + """\
 #ifndef VK_DISPATCH_TRAMPOLINES_H
 #define VK_DISPATCH_TRAMPOLINES_H
 
-#include "vulkan/util/vk_dispatch_table.h"
+#include "vk_dispatch_table.h"
 
 #ifdef __cplusplus
 extern "C" {