iio: chemical: bmp680: Drop unneeded explicit castings

In few places the unnecessary explicit castings are being used.
Drop them for good.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20210312134349.3472-1-andriy.shevchenko@linux.intel.com


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>