linux-nvml.c: Fix type warning.
linux-nvml.c: Fix type warning.

CUDA and NVML have an signed vs unsigned thing going on in their
returned device counts, cast away the warning.

pyrovski/papi,arm-hpc/papi,arm-hpc/papi,pyrovski/papi,pyrovski/papi,pyrovski/papi,arm-hpc/papi,pyrovski/papi,pyrovski/papi,arm-hpc/papi,arm-hpc/papi,arm-hpc/papi,pyrovski/papi,arm-hpc/papi,pyrovski/papi