ASoC: adau1701: refactor firmware loading function

Pass a struct i2c_client * to adau1701_load_firmware directly to make
the code more readable.

Signed-off-by: Daniel Mack <zonque@gmail.com>
Acked-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>