iio:pot:mcp41010: Switch to generic firmware properties.

In this case it was only of_device_get_match_data() + header update.
This enables use of other firmware types with no other changes, such
as ACPI via the PRP0001 route.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: Chris Coffey <cmc@babblebit.net>