iio:imu:mpu6050: Tidy up parameters to regmap_bulk functions.

A mixture of:
* Casts to u8 * for the val parameter which is void * and so needs no cast.
* Explicit sizes when we can use sizeof on the destination / source variable.

Not broken in anyway, I'm just trying to tidy up the is in the subsystem to
avoid it getting cut and paste into new drivers.
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>

drivers/iio/imu/inv_mpu6050/inv_mpu_core.c

@@ -526,7 +526,7 @@ static int inv_mpu6050_sensor_set(struct inv_mpu6050_state  *st, int reg,
 	__be16 d = cpu_to_be16(val);
 
 	ind = (axis - IIO_MOD_X) * 2;
-	result = regmap_bulk_write(st->map, reg + ind, (u8 *)&d, 2);
+	result = regmap_bulk_write(st->map, reg + ind, &d, sizeof(d));
 	if (result)
 		return -EINVAL;
 
@@ -540,7 +540,7 @@ static int inv_mpu6050_sensor_show(struct inv_mpu6050_state  *st, int reg,
 	__be16 d;
 
 	ind = (axis - IIO_MOD_X) * 2;
-	result = regmap_bulk_read(st->map, reg + ind, (u8 *)&d, 2);
+	result = regmap_bulk_read(st->map, reg + ind, &d, sizeof(d));
 	if (result)
 		return -EINVAL;
 	*val = (short)be16_to_cpup(&d);