perf tools: Fix incorrect fd error comparison

Zero is a valid fd.  Error comparison should check for negative fd.
Signed-off-by: NAdrian Hunter <adrian.hunter@intel.com>
Acked-by: NJiri Olsa <jolsa@kernel.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/1405586590-13657-2-git-send-email-adrian.hunter@intel.comSigned-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/dso.c

@@ -216,7 +216,7 @@ static int open_dso(struct dso *dso, struct machine *machine)
 {
 	int fd = __open_dso(dso, machine);
 
-	if (fd > 0) {
+	if (fd >= 0) {
 		dso__list_add(dso);
 		/*
 		 * Check if we crossed the allowed number