main: Use NumUniformBlocks to count UBOs

main: Use NumUniformBlocks to count UBOs

Now that we have separate index spaces for UBOs and SSBOs we do not need
to iterate through BufferInterfaceBlocks any more, we can just take the
UBO count directly from NumUniformBlocks.

Reviewed-by: Kristian Høgsberg <krh@bitplanet.net>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>