usb: phy: phy-rcar-gen2-usb: fix phy initialization

Add missing USB UGCTRL2 register offset.

Signed-off-by: Valentine Barshak <valentine.barshak@cogentembedded.com>
Acked-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Felipe Balbi <balbi@ti.com>