Make sure waiting processes are woken on modem-status changes.

Currently processes are only woken on termios changes regardless of
whether the modem status has changed.

Cc: stable <stable@vger.kernel.org>
Signed-off-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>