OMAP3: PM: USBHOST: clear wakeup events on both hosts

USBHOST module has 2 fclocks (for HOST1 and HOST2), only one iclock
and only a single bit in the WKST register to indicate a wakeup event.

Because of the single WKST bit, we cannot know whether a wakeup event
was on HOST1 or HOST2, so enable both fclocks before clearing the
wakeup event to ensure both hosts can properly clear the event.

Signed-off-by: Vikram Pandita <vikram.pandita@ti.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>