V4L/DVB (5871): Conexant 2388x: check for kthread_run

The patch adds checking of kthread_run return code and issues a message
if it fails.

Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>