[media] stk1160: Wait for completion of transfers to and from AC97 codec

The STK1160 needs some time to transfer data to and from the AC97 codec.
The transfer completion is indicated by command read/write bits in the
chip's audio control register. The driver should poll these bits and
wait until they have been cleared by hardware before trying to retrieve
the results of a read operation or setting a new write command.

[mchehab@s-opensource.com: make checkpatch happier]
Signed-off-by: Marcel Hasler <mahasler@gmail.com>
Acked-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>