V4L/DVB (4624): Tvaudio: Replaced kernel_thread() with kthread_run()

Replaced kernel_thread() with kthread_run() since kernel_thread() is
deprecated in drivers/modules.
Removed the completion and the wait queue which are now useless with
kthread. Also removed the allow_signal() call as signals don't apply
to kernel threads.
Fixed a small race condition when thread is stopped.
Please check if the timer vs. thread still works fine without the wait
queue.

Signed-off-by: Cedric Le Goater <clg@fr.ibm.com>
Signed-off-by: Michael Krufky <mkrufky@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>