powerpc/usb: fix usb CTRL_PHY_CLK_VALID breaks on some platform
Fix checking of CTRL_PHY_CLK_VALID bit break on some platform on which
there is not USB CTRL_PHY_CLK_VALID bit.
- P1023/P3041/P5020 etc,have this bit
- P3060/4080/PSC913x do have this bit, but not mentioned in RM.
- P1022(perhaps and other) has no this bit