ASoC: rockchip: spdif: Mark SPDIF_SMPDR as volatile

This patch marks SPDIF_SMPDR as volatile to make it resaonable,
which also requires marking it as readable, even though it isn't.
Signed-off-by: Sugar Zhang <sugar.zhang@rock-chips.com>
Link: https://lore.kernel.org/r/1629800162-12824-2-git-send-email-sugar.zhang@rock-chips.comSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/rockchip/rockchip_spdif.c

@@ -247,6 +247,7 @@ static bool rk_spdif_rd_reg(struct device *dev, unsigned int reg)
 	case SPDIF_INTCR:
 	case SPDIF_INTSR:
 	case SPDIF_XFER:
+	case SPDIF_SMPDR:
 		return true;
 	default:
 		return false;
@@ -258,6 +259,7 @@ static bool rk_spdif_volatile_reg(struct device *dev, unsigned int reg)
 	switch (reg) {
 	case SPDIF_INTSR:
 	case SPDIF_SDBLR:
+	case SPDIF_SMPDR:
 		return true;
 	default:
 		return false;