phy: rockchip-usb: Fixup rockchip_usb_phy_power_on failure path

If rockchip_usb_phy_power() fails, we need to call clk_disable_unprepare()
before return. This is to ensure we have balanced clk_enable/disable calls.
Also remove unneeded ret checking in rockchip_usb_phy_power_off.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>