perf probe: Fix to show correct error string

Fix perf probe to show correct error string when it
fails to delete an event. The write(2) returns -1
if failed, and errno stores real error number.

Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: stable@kernel.org
Link: http://lkml.kernel.org/r/20111004104504.14591.41266.stgit@fedora15
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

tools/perf/util/probe-event.c

@@ -1956,8 +1956,10 @@ static int __del_trace_probe_event(int fd, struct str_node *ent)
 
 	pr_debug("Writing event: %s\n", buf);
 	ret = write(fd, buf, strlen(buf));
-	if (ret < 0)
+	if (ret < 0) {
+		ret = -errno;
 		goto error;
+	}
 
 	printf("Remove event: %s\n", ent->s);
 	return 0;