usb: renesas_usbhs: fixup device_register timing

current renesas_usbhs is using new style udc_start/stop from
af1d7056
(usb: gadget: renesas: convert to new style).

But bind() function will fail if it was called before
device_register() (or device_add()).
This patch modifies this issue.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>