USB: cdc-acm: fix TIOCMIWAIT

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: 5a6a62bdb9 ("cdc-acm: add TIOCMIWAIT")
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Johan Hovold <johan@kernel.org>
Acked-by: Oliver Neukum <oneukum@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/class/cdc-acm.c

@@ -932,8 +932,6 @@ static int wait_serial_change(struct acm *acm, unsigned long arg)
 	DECLARE_WAITQUEUE(wait, current);
 	struct async_icount old, new;
 
-	if (arg & (TIOCM_DSR | TIOCM_RI | TIOCM_CD))
-		return -EINVAL;
 	do {
 		spin_lock_irq(&acm->read_lock);
 		old = acm->oldcount;