anv: fix assert to build with shader cache disabled

When setting -Dshader-cache=disabled the build fails due
no member named 'disk_cache' in 'struct anv_physical_device'

Signed-off-by: sjfricke <spencerfricke@gmail.com>
Reviewed-by: Tapani Pälli <tapani.palli@intel.com>
Fixes: 7f1e8230 ("anv: Switch to the new common pipeline cache")
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/18181>

src/intel/vulkan/anv_device.c

@@ -606,7 +606,7 @@ anv_physical_device_free_disk_cache(struct anv_physical_device *device)
       device->vk.disk_cache = NULL;
    }
 #else
-   assert(device->disk_cache == NULL);
+   assert(device->vk.disk_cache == NULL);
 #endif
 }