[media] tvp5150: make read operations atomic

Instead of using two I2C operations between write and read,
use just one i2c_transfer. That allows I2C mutexes to not
let any other I2C transfer between the two.

Reviewed-by: Frank Schäfer <fschaefer.oss@googlemail.com>
Tested-by: Frank Schäfer <fschaefer.oss@googlemail.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>