V4L/DVB (5074): Some fixes at stream waitqueue on vivi

There are several potential troubles on vivi waitqueue code:
- Watchdog timer should be reset at every received frame;
- Watchdog timer should be reset at the beginning of vivi_thread();
- Checks for errors when creating a newer thread with kernel_thread();
- Wake up vivi_thread() after creating it.

Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>