perf/x86/intel/uncore: Fix missing marker for snr_uncore_imc_freerunning_events

An Oops during the boot is found on some SNR machines.  It turns out
this is because the snr_uncore_imc_freerunning_events[] array was
missing an end-marker.

Fixes: ee49532b ("perf/x86/intel/uncore: Add IMC uncore support for Snow Ridge")
Reported-by: Like Xu <like.xu@linux.intel.com>
Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Tested-by: Like Xu <like.xu@linux.intel.com>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20200116200210.18937-1-kan.liang@linux.intel.com