perf_event.c: Check return value of ioctl
perf_event.c: Check return value of ioctl

Thanks to Will Cohen for reporting based upon output of coverity.

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