USB: gadget: fix build error in omap_apollon_2420_defconfig

In apollon case, it only used udc, so udc configuration should select
USB_OTG_UTILS also.

Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Acked-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>