phy: renesas: rcar-gen3-usb2: unify OBINTEN handling

This patch unifies the OBINTEN handling to clean-up the code.

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>