perf pmu: fix alias->snapshot missing initialization bug

This patch fixes a bug in __perf_pmu__new_alias() whereby the
alias->snapshot field was not initialized to false. This led to random
alias->snapshot value for an alias and was breaking some measurements
such as:

  $ perf stat -a -e uncore_imc/data_reads/ -I 1000 sleep 100

Because the event ended up being treated as snapshot mode, when it is
not.

Signed-off-by: Stephane Eranian <eranian@google.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1452106201-13073-1-git-send-email-eranian@google.com


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>