pvr: Fix PDS temps allocation on fragment stage

pvr: Fix PDS temps allocation on fragment stage

Previously the USC temps count was incorrectly being used for the
PDS temps count.

It was causing:
  csbgen/pvr_packet_helpers.h:79:
    __pvr_uint: Assertion `v <= max' failed.

This fixes the assert being hit on:
  dEQP-VK.ubo.random.basic_arrays.2
  dEQP-VK.ubo.random.all_shared_buffer.3
  dEQP-VK.ubo.random.all_shared_buffer.48
  dEQP-VK.ubo.random.all_out_of_order_offsets.3

This does not fully fix the tests though.

Signed-off-by: Karmjit Mahil <Karmjit.Mahil@imgtec.com>
Reviewed-by: Matt Coster <matt.coster@imgtec.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/23356>