ASoC: SOF: imx8m: Constify snd_sof_dsp_ops

'struct snd_sof_dsp_ops' is not modified by core code, so it can be made
const for increased code safety.

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-v2-9-e553fe67ae82@kernel.org


Signed-off-by: Mark Brown <broonie@kernel.org>