usb: dwc3: gadget: initialize NUMP based on RxFIFO Size

Instead of using burst size to configure NUMP, we
should be using RxFIFO Size instead. DWC3 is smart
enough to know that it shouldn't burst in case burst
size is 0.

Reported-by: John Youn <johnyoun@synopsys.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>