USB: option: fix memory leak

Fix memory leak introduced by commit 383cedc3

 ("USB: serial:
full autosuspend support for the option driver") which allocates
usb-serial data but never frees it.

Cc: stable <stable@vger.kernel.org>
Signed-off-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>