Fix bug accumulating nrank_pp_intranode on PME ranks

The old code led to cr->nrank_pp_intranode=zero on PME ranks, which
meant that a command line of mpirun -np 4 mdrun -npme 2 on a two-GPU
node would fail, because gmx_select_gpu_ids() runs on all ranks, and
it calls limit_num_gpus_used() which thinks 0 PP ranks and 2 GPUs is
silly. Adding -gpu_id 01 works, of course, but that takes a different
code path in gmx_select_gpu_ids().

Change-Id: Iecd43ef9b71e2cc0339e93724b6b1071f0a159f6