USB: Fix goku_udc usb speed handling

The usb gadget framework revealed weakness in the godu_udc
gadget driver register function. Instead of checking if
speed asked for was USB_LOW_SPEED upon usb_gadget_register()
to deny service, it checked only for USB_FULL_SPEED, thus
denying service to usb high speed capable gadgets.

Signed-off-by: SangSu Park <sangsu@gmail.com>
Acked-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>