cdc-acm: ensure that termios get set when the port is activated

The driver wasn't properly configuring the hardware for the current
termios settings under all conditions.  Ensure that termios are
written to the device when the port is activated.

Signed-off-by: Jim Paris <jim@jtan.com>
Reviewed-by: Johan Hovold <johan@kernel.org>
Acked-by: Oliver Neukum <oneukum@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>