perf/x86/intel/uncore: Fix the build on !CONFIG_PHYS_ADDR_T_64BIT

'val2' is unused if !CONFIG_PHYS_ADDR_T_64BIT:

  arch/x86/events/intel/uncore_discovery.c:213:18: error: unused variable ‘val2’ [-Werror=unused-variable]

Signed-off-by: Ingo Molnar <mingo@kernel.org>