iio: light: bh1780: use mod_devicetable.h and drop of_match_ptr macro

Whilst this enables ACPI binding or the device via PRP0001 the
primary aim is to remove potential for these two things to be
cut and paste into new drivers.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Alexandru Ardelean <alexandru.ardelean@analog.com>