Fix warning in papi_libpfm4_events.c
Fix warning in papi_libpfm4_events.c

We were setting a value but never using it.

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