perf bench: Fix 2 memory sanitizer warnings

perf bench: Fix 2 memory sanitizer warnings

Memory sanitizer warns if a write is performed where the memory being
read for the write is uninitialized. Avoid this warning by initializing
the memory.

Signed-off-by: Ian Rogers <irogers@google.com>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lore.kernel.org/lkml/20200912053725.1405857-1-irogers@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>