perf test workload thloop: Make count increments atomic

perf test workload thloop: Make count increments atomic

The count variable is incremented by multiple threads, doing so
without an atomic operation causes thread sanitizer warnings. Switch
to using relaxed atomics.

Signed-off-by: Ian Rogers <irogers@google.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20230114215251.271678-1-irogers@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>