clk: rockchip: rk3328: Handle usb480m phy clock

Handle USB480M clock ID in set_rate() and set_parent()
to allow the dt assigned-clocks and assigned-clock-parents
work on rk3328.dtsi

Cc: Lukasz Majewski <lukma@denx.de>
Cc: Sean Anderson <seanga2@gmail.com>
Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>