drm/nouveau/gr/gf117-: read NV_PGRAPH_GPC_GPM_PD_PES_TPC_ID_MASK from correct GPC

Each GPCCS unit was reading the mask from GPC0, which causes problems on
boards where some GPCs are missing PPCs.

Part of the fix for fdo#92761.

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>