perf utils: Check verbose flag properly

It now can have negative value to suppress the message entirely.  So it
needs to check it being positive.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: kernel-team@lge.com
Link: http://lkml.kernel.org/r/20170217081742.17417-3-namhyung@kernel.org
[ Adjust fuzz on tools/perf/util/pmu.c, add > 0 checks in many other places ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-top.c

@@ -871,7 +871,7 @@ try_again:
 		if (perf_evsel__open(counter, top->evlist->cpus,
 				     top->evlist->threads) < 0) {
 			if (perf_evsel__fallback(counter, errno, msg, sizeof(msg))) {
-				if (verbose)
+				if (verbose > 0)
 					ui__warning("%s\n", msg);
 				goto try_again;
 			}