regmap: cache: Provide a get address of value operation

Provide a helper to do the size based index into a block of registers and
use it when reading a value.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
diff --git a/drivers/base/regmap/regcache.c b/drivers/base/regmap/regcache.c
index 0f4fb8b..229c804 100644
--- a/drivers/base/regmap/regcache.c
+++ b/drivers/base/regmap/regcache.c
@@ -458,8 +458,8 @@
 
 	/* Use device native format if possible */
 	if (map->format.parse_val)
-		return map->format.parse_val(base +
-					     (map->cache_word_size * idx));
+		return map->format.parse_val(regcache_get_val_addr(map, base,
+								   idx));
 
 	switch (map->cache_word_size) {
 	case 1: {