USB: fix buffer overflows with parsing CDC headers

Parsing CDC headers a buffer overflow cannot just be prevented
by checking that the remainder of the buffer is longer than minimum
length. The size of the fields to be parsed must be figured in, too.

In newer kernels this issue has been fixed at a central location with

commit 2e1c42391ff2556387b3cb6308b24f6f65619feb
Author: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Date:   Thu Sep 21 16:58:48 2017 +0200

    USB: core: harden cdc_parse_cdc_header

on anything older the parsing had not been centralised, so a separate
fix for each driver is necessary.

Change-Id: I5b3095ebb52c92c69d363f09e5f2f981188f7d62
Signed-off-by: Oliver Neukum <oneukum@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>