ASoC: wm_adsp: Improve variable naming

We have wm_adsp_region, wm_adsp_alg_region, and wmfw_region, the
variables for which are all frequently called region, this can get quite
confusing when reviewing the code especially given some functions are
quite long. Consistently use mem for wm_adsp_regions, alg_region for
wm_adsp_alg_region and region for wmfw_region.

Additionally, we use a mix of adsp and dsp for pointers to the wm_adsp
structure standardise this on dsp.

Finally, we use algs to refer to the number of algorithms quite
frequently, change this to the more descriptive n_algs.

Signed-off-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@kernel.org>