usb: dwc3: gadget: Remove descriptor arguments to ep_enable

The __dwc3_gadget_endpoint_enable() function has access to the endpoint
descriptors via the usb_ep. So we don't need to pass them in as
arguments. The descriptors should be set by the caller prior to calling
usb_ep_enable().

Signed-off-by: John Youn <johnyoun@synopsys.com>

[felipe.balbi@linux.intel.com : minor improvements]

Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>