usb: gadget: renesas_usbhs: fixup driver compile style

In current renesas-usbhs,
there was inconsistency about the style of kernel module or built-in.
This patch solve it.

[ balbi@ti.com : fix compile issue when building modules ]

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