V4L/DVB (6279): en_50221: convert to kthread API

Here's an attempted update to the full kthread API + wake_up_process:

Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
CC: Andrew de Quincey <adq_dvb@lidskialf.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>