USB: at91-ohci, handle extra at91sam9261 ahb clock

The AT91SAM9261 needs to activate an AHB clock (HCK0) to use the USB Host
controller. Previously clock.c would just enable it at startup, but now
all the unused clocks are automatically disabled.

Based on patch from Nicolas Ferre.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>