ASoC: wm_adsp: Sanitize parameter passing

No need to hold on to the `codec' pointer.  We can use the `dsp'
pointer and grab all the information we need from there.  This
makes the parameters for the functions a bit more sane and idiomatic.

Signed-off-by: Dimitris Papastamos <dp@opensource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@linaro.org>