cdc-acm: remove is_int_ep from acm structure

is_int_ep is used only in acm_probe, no need to store it in device data.

Signed-off-by: Ladislav Michl <ladis@linux-mips.org>
Acked-by: Oliver Neukum <oneukum@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>