regmap: Use helper function for register offset

As a helper function exists for calculating register offsets lets use
that rather than open coding with the reg_stride.
Signed-off-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/base/regmap/regmap.c

@@ -1993,7 +1993,7 @@ int regmap_bulk_write(struct regmap *map, unsigned int reg, const void *val,
 				return -EINVAL;
 			}
 
-			ret = regmap_write(map, reg + (i * map->reg_stride),
+			ret = regmap_write(map, reg + regmap_get_offset(map, i),
 					   ival);
 			if (ret)
 				return ret;