phy: lpc18xx-usb-otg: fix clock order in phy init

Changing the frequency of the USB clock must be done before the
PLL is powered on (prepared). This matters when the USB clock
is not setup by either boot ROM or boot loader. Reorder the
function calls to adhere to the order noted in the user manual.

Signed-off-by: Joachim Eastwood <manabian@gmail.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>