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
(Wanted to examine the NIR code, but I learned about MESA_SHADER_CACHE_DISABLE
now, but decided to push this patch)
Signed-off-by: sjfricke spencerfricke@gmail.com