V4L/DVB (5724): Saa7134-tvaudio: kthread conversion

Acked-by: Hermann Pitton <hermann-pitton@arcor.de>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>