ASoC: fsl: Constify reg_default array

Static 'struct reg_default' array is not modified so can be changed to
const for more safety.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://patch.msgid.link/20250528-asoc-const-unused-v1-2-19a5d07b9d5c@linaro.org


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