ASoC: tegra: Fix uninitialized flat cache warning in tegra210_ahub

The tegra210_ahub driver started triggering a warning after commit
e062bdf ("regmap: warn users about uninitialized flat cache"),
which flags drivers using REGCACHE_FLAT without register defaults.
Since the driver omits default definitions because its registers are
zero initialized, the following warning is shown:

  WARNING KERN tegra210-ahub 2900800.ahub: using zero-initialized flat cache, this may cause unexpected behavior

Switch to REGCACHE_FLAT_S which is the recommended cache type for
sparse register maps without defaults. This cache type initializes
entries on-demand from hardware, eliminating the warning while using
memory efficiently.

Signed-off-by: sheetal <sheetal@nvidia.com>
Link: https://patch.msgid.link/20251208052040.4025612-1-sheetal@nvidia.com
Signed-off-by: Mark Brown <broonie@kernel.org>

Author: sheetal

sound/soc/tegra/tegra210_ahub.c

@@ -2077,15 +2077,15 @@ static const struct regmap_config tegra210_ahub_regmap_config = {
 	.val_bits		= 32,
 	.reg_stride		= 4,
 	.max_register		= TEGRA210_MAX_REGISTER_ADDR,
-	.cache_type		= REGCACHE_FLAT,
+	.cache_type		= REGCACHE_FLAT_S,
 };
 
 static const struct regmap_config tegra186_ahub_regmap_config = {
 	.reg_bits		= 32,
 	.val_bits		= 32,
 	.reg_stride		= 4,
 	.max_register		= TEGRA186_MAX_REGISTER_ADDR,
-	.cache_type		= REGCACHE_FLAT,
+	.cache_type		= REGCACHE_FLAT_S,
 };
 
 static const struct regmap_config tegra264_ahub_regmap_config = {
@@ -2094,7 +2094,7 @@ static const struct regmap_config tegra264_ahub_regmap_config = {
 	.reg_stride		= 4,
 	.writeable_reg		= tegra264_ahub_wr_reg,
 	.max_register		= TEGRA264_MAX_REGISTER_ADDR,
-	.cache_type		= REGCACHE_FLAT,
+	.cache_type		= REGCACHE_FLAT_S,
 };
 
 static const struct tegra_ahub_soc_data soc_data_tegra210 = {