usb: gadget: udc: dummy: make use of new usb_endpoint_maxp_mult()

We have introduced a helper to calculate multiplier
value from wMaxPacketSize. Start using it.

Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: <linux-usb@vger.kernel.org>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/gadget/udc/dummy_hcd.c

@@ -1483,8 +1483,7 @@ static int periodic_bytes(struct dummy *dum, struct dummy_ep *ep)
 		int	tmp;
 
 		/* high bandwidth mode */
-		tmp = usb_endpoint_maxp(ep->desc);
-		tmp = (tmp >> 11) & 0x03;
+		tmp = usb_endpoint_maxp_mult(ep->desc);
 		tmp *= 8 /* applies to entire frame */;
 		limit += limit * tmp;
 	}