perf test mmap-thread-lookup: Initialize variable to suppress memory sanitizer warning

Running the 'perf test' command after building perf with a memory
sanitizer causes a warning that says:

  WARNING: MemorySanitizer: use-of-uninitialized-value... in mmap-thread-lookup.c

Initializing the go variable to 0 silences this harmless warning.

Committer warning:

This was harmless, just a simple test writing whatever was at that
sizeof(int) memory area just to signal another thread blocked reading
that file created with pipe(). Initialize it tho so that we don't get
this warning.
Signed-off-by: Numfor Mbiziwo-Tiapo <nums@google.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mark Drayton <mbd@fb.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Song Liu <songliubraving@fb.com>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/20190702173716.181223-1-nums@google.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/tests/mmap-thread-lookup.c

@@ -53,7 +53,7 @@ static void *thread_fn(void *arg)
 {
 	struct thread_data *td = arg;
 	ssize_t ret;
-	int go;
+	int go = 0;
 
 	if (thread_init(td))
 		return NULL;