USB: option: fix memory leak

commit b9c3aab315b51f81649a0d737c4c73783fbd8de0 upstream.

Fix memory leak introduced by commit 383cedc3bb435de7a2 ("USB: serial:
full autosuspend support for the option driver") which allocates
usb-serial data but never frees it.

Signed-off-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>