BugLink: https://bugs.launchpad.net/bugs/1791942

commit 1445cbe4 upstream.

The device (a POS terminal) implements CDC ACM, but has not union
descriptor.
Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
Acked-by: Oliver Neukum <oneukum@suse.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>