regmap: Fix the size calculation for map->format.buf_size

The word to be transmitted/received via regmap is composed by the following
parts:

config->reg_bits
config->val_bits
config->pad_bits

,so the total size should be calculated by summing up the number of bits of
each element and using a DIV_ROUND_UP to return the number of bytes.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

drivers/base/regmap/regmap.c

@@ -246,11 +246,11 @@ struct regmap *regmap_init(struct device *dev,
 		map->lock = regmap_lock_mutex;
 		map->unlock = regmap_unlock_mutex;
 	}
-	map->format.buf_size = (config->reg_bits + config->val_bits) / 8;
 	map->format.reg_bytes = DIV_ROUND_UP(config->reg_bits, 8);
 	map->format.pad_bytes = config->pad_bits / 8;
 	map->format.val_bytes = DIV_ROUND_UP(config->val_bits, 8);
-	map->format.buf_size += map->format.pad_bytes;
+	map->format.buf_size = DIV_ROUND_UP(config->reg_bits +
+			config->val_bits + config->pad_bits, 8);
 	map->reg_shift = config->pad_bits % 8;
 	if (config->reg_stride)
 		map->reg_stride = config->reg_stride;