OMAP1: OMAP_TAG_USB buildfix (OSK)

OMAP1: OMAP_TAG_USB buildfix (OSK)

Build fix:

  CC      arch/arm/mach-omap1/board-osk.o
  arch/arm/mach-omap1/board-osk.c: In function 'osk_mistral_init':
  arch/arm/mach-omap1/board-osk.c:512: error: implicit declaration of function 'omap_usb_init'
  make[1]: *** [arch/arm/mach-omap1/board-osk.o] Error 1

The error is twofold.  First, USB is on the mainboard, not the Mistral card;
that's specific to the OSK.  Second, header goofage -- hurts all OMAP1 boards.

I'm puzzled by the notion tha the "OMAP1: get rid of OMAP_TAG_USB" patch could
have been compile-tested.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Tony Lindgren <tony@atomide.com>