V4L/DVB (5209): Kthread api conversion for dvb_frontend and av7110 fix

avoid double-up(), pointed out by Oliver.

Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Oliver Endriss <o.endriss@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>