ASoC: mchp-spdifrx: use single tab indent for structure

Use single tab indentation for mchp_spdifrx_mixer_control structure.
Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Link: https://lore.kernel.org/r/20220725130925.1781791-3-claudiu.beznea@microchip.comSigned-off-by: Mark Brown <broonie@kernel.org>