usb: gadget: udc: renesas_usb3: fix zlp transfer by the dmac

The dedicated dmac can transfer a zero-length-packet (zlp) if some bits
of the USB_COM_CON register. However, the commit 2d4aa21a ("usb:
gadget: udc: renesas_usb3: add support for dedicated DMAC") didn't set
the bits to 1. So, this patch fixes it.

Fixes: 2d4aa21a ("usb: gadget: udc: renesas_usb3: add support for dedicated DMAC)
Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>