USB: fsl/ehci: fix failure of checking PHY_CLK_VALID during reinitialization

In case of usb phy reinitialization:
e.g. insmod usb-module(usb works well) -> rmmod usb-module -> insmod usb-module
It found the PHY_CLK_VALID bit didn't work if it's not with the power-on reset.
So we just check PHY_CLK_VALID bit during the stage with POR, this can be met
by the tricky of checking FSL_SOC_USB_PRICTRL register.

Signed-off-by: Shengzhou Liu <Shengzhou.Liu@freescale.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>