ASoC: SOF: Constify stored pointer to snd_sof_dsp_ops

ASoC: SOF: Constify stored pointer to snd_sof_dsp_ops

The core code does not modify the 'struct snd_sof_dsp_ops', stored in
'struct sof_dev_desc'.  Make the pointer to 'struct snd_sof_dsp_ops'
const to annotate this, make code a bit safer and allow individual
drivers to also define this structure as const.

Tested-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20240426-n-const-ops-var-v2-4-e553fe67ae82@kernel.org
Signed-off-by: Mark Brown <broonie@kernel.org>