V4L/DVB: cx23885: Check for slave nack on all transactions

Don't just check for nacks on zero-length transactions. Check on
other transactions too.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Andy Walls <awalls@md.metrocast.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>