Get the "usb-bus" clock and ensure it is enabled
when the OHCI core is in use.

It seems that a few bootloaders do not enable the
UPLL at startup, which stops the OHCI core having
a 48MHz bus clock. The improvements to the clock
framework for the s3c24xx now allow the USB PLL
to be started and stopped when being used.
Signed-off-by: NBen Dooks <ben-linux@fluff.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>