usb: gadget: f_uac1: silence an info leak warning

Smatch complains that "len" could be larger than the sizeof(value)
so we could be copying garbage here.  I have changed this to match
how things are done in composite_setup().

The call tree looks like:
  composite_setup()
  --> f_audio_setup()
      --> audio_get_intf_req()

composite_setup() expects the return value to be set to
sizeof(value).
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/gadget/f_uac1.c

@@ -418,6 +418,7 @@ static int audio_get_intf_req(struct usb_function *f,
 
 	req->context = audio;
 	req->complete = f_audio_complete;
+	len = min_t(size_t, sizeof(value), len);
 	memcpy(req->buf, &value, len);
 
 	return len;