Input: ad7879 - use i2c_smbus_read_i2c_block_data() to lower overhead

static int ad7879_i2c_multi_read(struct device *dev,

				 u8 first_reg, u8 count, u16 *buf)

{

	struct i2c_client *client = to_i2c_client(dev);

	u8 idx;

	i2c_smbus_read_i2c_block_data(client, first_reg, count * 2, (u8 *)buf);

	for (idx = 0; idx < count; ++idx)

		buf[idx] = ad7879_i2c_read(dev, first_reg + idx);

		buf[idx] = swab16(buf[idx]);

	return 0;

}