USB: cdc-acm: fix TIOCMIWAIT

USB: cdc-acm: fix TIOCMIWAIT

commit 18266403f3fe507f0246faa1d5432333a2f139ca upstream.

The TIOCMIWAIT implementation would return -EINVAL if any of the three
supported signals were included in the mask.

Instead of returning an error in case TIOCM_CTS is included, simply
drop the mask check completely, which is in accordance with how other
drivers implement this ioctl.

Fixes: 5a6a62bdb925 ("cdc-acm: add TIOCMIWAIT")
Signed-off-by: Johan Hovold <johan@kernel.org>
Acked-by: Oliver Neukum <oneukum@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>