iio:chemical:atlas-sensor: Drop unnecessary explicit casts in regmap_bulk_read calls

regmap_bulk_read takes a void * for its val parameter. It certainly
makes no sense to cast to a (u8 *) + no need to explicitly cast
at all when converting another pointer type to void *.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Acked-by: Matt Ranostay <matt.ranostay@konsulko.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Reviewed-by: Alexandru Ardelean <alexandru.ardelean@analog.com>