ezusb: add dependency to USB

This fixes an error during modpost, when ezusb is built into the kernel
while USB is built as module.

Signed-off-by: René Bürgel <rene.buergel@sohard.de>
Cc: stable <stable@vger.kernel.org>
--
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>