iio:magn:mmc35240: Drop unnecessary casts of val parameter in regmap_bulk*

Given the parameter is void *, casting to u8 * is unnecessary.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Daniel Baluta <daniel.baluta@gmail.com>
Reviewed-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>