phy: rcar-gen3-usb2: remove unnecesary struct rcar_gen3_data

Since this driver uses the struct rcar_gen3_data in struct rcar_gen3_chan
only, we can remove the rcar_gen3_data.

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>