regmap: Handle sparse caches in the default sync

If there is no cache entry available we will get -ENOENT from the cache
implementation, handle this gracefully and skip rather than treating it as
an error.

Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20230325-regcache-sparse-sync-v1-1-2a890239d061@kernel.org

drivers/base/regmap/regcache.c

@@ -311,6 +311,8 @@ static int regcache_default_sync(struct regmap *map, unsigned int min,
 			continue;
 
 		ret = regcache_read(map, reg, &val);
+		if (ret == -ENOENT)
+			continue;
 		if (ret)
 			return ret;