[media] cx231xx: use 1 byte read for i2c scan

Now cx231xx_i2c_check_for_device works like i2c_check_for_device of em28xx driver.

For me this fixes scanning of all ports but port 2.

Signed-off-by: Matthias Schwarzott <zzam@gentoo.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>