usb: musb: 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.

Link: https://lkml.kernel.org/r/20220705224750.532345354@goodmis.org

Cc: Bin Liu <b-liu@ti.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: linux-usb@vger.kernel.org
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

drivers/usb/musb/musb_trace.h

@@ -28,11 +28,11 @@ TRACE_EVENT(musb_log,
 	TP_ARGS(musb, vaf),
 	TP_STRUCT__entry(
 		__string(name, dev_name(musb->controller))
-		__dynamic_array(char, msg, MUSB_MSG_MAX)
+		__vstring(msg, vaf->fmt, vaf->va)
 	),
 	TP_fast_assign(
 		__assign_str(name, dev_name(musb->controller));
-		vsnprintf(__get_str(msg), MUSB_MSG_MAX, vaf->fmt, *vaf->va);
+		__assign_vstr(msg, vaf->fmt, vaf->va);
 	),
 	TP_printk("%s: %s", __get_str(name), __get_str(msg))
 );