phy: rockchip-inno-usb2: correct clk_ops callback

Since we needs to delay ~1ms to wait for 480MHz output clock
of USB2 PHY to become stable after turn on it, the delay time
is pretty long for something that's supposed to be "atomic"
like a clk_enable(). Consider that clk_enable() will disable
interrupt and that a 1ms interrupt latency is not sensible.

The 480MHz output clock should be handled in prepare callbacks
which support gate a clk if the operation may sleep.

Signed-off-by: William Wu <wulf@rock-chips.com>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>