[media] au8522: move input_mode out one level

The input mode is used not only inside the setup_decoder_defaults()
but also at au8522_*_mode routines.

So, move it one level up. As an advantage, we can now group the
function that sets the input into just one.

Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>