usb: gadget: renesas_usbhs: tidyup mod_host request variable name

renesas_usbhs driver use "req" for struct usb_ctrlrequest,
and "ureq" for struct usbhsh_request

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>