USB: spcp8x5: fix use-after-free in TIOCMIWAIT

USB: spcp8x5: fix use-after-free in TIOCMIWAIT

commit d1baabc8006fd238ad8da4d734dc815a8de02362 upstream.

commit dbcea7615d8d7d58f6ff49d2c5568113f70effe9 upstream.

Use the port wait queue and make sure to check the serial disconnected
flag before accessing private port data after waking up.

This is is needed as the private port data (including the wait queue
itself) can be gone when waking up after a disconnect.

Signed-off-by: Johan Hovold <jhovold@gmail.com>
[bwh: Backported to 3.2: adjust context, indentation]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Cc: Yang Yingliang <yangyingliang@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>