USB: mtu3: tracing: Use the new __vstring() helper

Instead of open coding a __dynamic_array() with a fixed length (which
defeats the purpose of the dynamic array in the first place). Use the new
__vstring() helper that will use a va_list and only write enough of the
string into the ring buffer that is needed.

Cc: Chunfeng Yun <chunfeng.yun@mediatek.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: linux-usb@vger.kernel.org
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-mediatek@lists.infradead.org
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

drivers/usb/mtu3/mtu3_trace.h

@@ -25,11 +25,11 @@ TRACE_EVENT(mtu3_log,
 	TP_ARGS(dev, vaf),
 	TP_STRUCT__entry(
 		__string(name, dev_name(dev))
-		__dynamic_array(char, msg, MTU3_MSG_MAX)
+		__vstring(msg, vaf->fmt, vaf->va),
 	),
 	TP_fast_assign(
 		__assign_str(name, dev_name(dev));
-		vsnprintf(__get_str(msg), MTU3_MSG_MAX, vaf->fmt, *vaf->va);
+		__assign_vstr(msg, vaf->fmt, vaf->va);
 	),
 	TP_printk("%s: %s", __get_str(name), __get_str(msg))
 );