ASoC: wm_adsp: Simplify handling of alg offset and length

The current code that reads the algorithm list from the DSP is
somewhat unclear, it converts directly from bytes to registers using
a hard coded divide by 2. Most offsets are usually handled in DSP
words within the driver and there is a function specifically for
converting from words to register addresses. So update the handling
to use these. This also removes the assumption that the registers
are 16-bit word addressed, which will no longer be true on some of
our newer parts.

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