usb: isp1760: Pass resource pointer to isp1760_register

The function takes quite a few arguments, passing the resource pointer
instead of the start address and length simplifies it a bit.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>