Fix format string bug in DBus::Error.

BUG=chromium:635879
TEST=None.

Change-Id: If3a344b08426bec971943942c548eadbbe16c01c
Reviewed-on: https://chromium-review.googlesource.com/367270
Commit-Ready: Ricky Zhou <rickyz@chromium.org>
Tested-by: Ricky Zhou <rickyz@chromium.org>
Reviewed-by: Jorge Lucangeli Obes <jorgelo@chromium.org>
Reviewed-by: Ricky Zhou <rickyz@chromium.org>

src/error.cpp

diff --git a/src/error.cpp b/src/error.cpp
index c34430b..4333537 100644
--- a/src/error.cpp
+++ b/src/error.cpp
@@ -79,7 +79,7 @@
 
 void Error::set(const char *name, const char *message)
 {
-	dbus_set_error(&(_int->error), name, message);
+	dbus_set_error(&(_int->error), name, "%s", message);
 }
 
 const char *Error::what() const throw()