Small fix in Perlmutter GPU sbatch script

[aeriforme]

Changes in Perlmutter GPU job script:
from #SBATCH --cpus-per-task=16 to #SBATCH --cpus-per-task=32.

This is to request (v)cores in consecutive blocks.

GPU 3 is closest to CPU cores 0-15, 64-79,
GPU 2 to CPU cores 16-31, 80-95,
...

If --cpus-per-task=16, MPI ranks 0 and 1 are mapped to cores 0 and 8.
If --cpus-per-task=32, MPI ranks 0 and 1 are mapped to cores 0 and 16.

Visual representation

@ax3l @WeiqunZhang is this correct?

[WeiqunZhang]

I think export OMP_NUM_THREADS=${SLURM_CPUS_PER_TASK} should be updated too, because SLURM_CPUS_PER_TASK is 32 now. We might want to simply set it to 16.