perf probe: Propagate error code when write(2) failed

When it failed to write probe commands to the probe_event file in
debugfs, it needs to propagate the error code properly.  Current code
blindly uses the return value of the write(2) so it always uses
-1 (-EPERM) and it might confuse users.
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1420886028-15135-4-git-send-email-namhyung@kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/probe-event.c

@@ -2052,10 +2052,12 @@ static int write_probe_trace_event(int fd, struct probe_trace_event *tev)
 	pr_debug("Writing event: %s\n", buf);
 	if (!probe_event_dry_run) {
 		ret = write(fd, buf, strlen(buf));
-		if (ret <= 0)
+		if (ret <= 0) {
+			ret = -errno;
 			pr_warning("Failed to write event: %s\n",
 				   strerror_r(errno, sbuf, sizeof(sbuf)));
 		}
+	}
 	free(buf);
 	return ret;
 }