USB: cdc-acm: fix pipe type of write endpoint

commit c5211187f7ff8e8dbff4ebf7c011ac4c0ffe319c upstream.

If the write endpoint is interrupt type, usb_sndintpipe() should
be passed to usb_fill_int_urb() instead of usb_sndbulkpipe().

Cc: Oliver Neukum <oneukum@suse.de>
Signed-off-by: Ming Lei <ming.lei@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>