usb: gadget: udc: renesas_usb3: fix device leak at unbind

usb: gadget: udc: renesas_usb3: fix device leak at unbind

Make sure to drop the reference to the companion device taken during
probe when the driver is unbound.

Fixes: 39facfa01c9f ("usb: gadget: udc: renesas_usb3: Add register of usb role switch")
Cc: stable@vger.kernel.org	# 4.19
Cc: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20250724091910.21092-4-johan@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>