In sys/dev/hwpmc/hwpmc_amd.c, fix a clang warning about invalid enum conversions.
In sys/dev/hwpmc/hwpmc_amd.c, fix a clang warning about invalid enum
conversions.

Reviewed by:	jkoshy
MFC after:	1 week

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase