iio: adc: mcp320x: Drop vendorless compatible strings

iio: adc: mcp320x: Drop vendorless compatible strings

The vendorless compatible strings are deprecated and weren't retained
when the binding was converted to schema. As a result, they are listed
as undocumented when running "make dt_compatible_check". Rather than add
them back to the schema, let's just drop them as they are unnecessary.
Furthermore, they are unnecessary as the SPI matching will strip the
vendor prefix on compatible string and match that against the
spi_device_id table.

Signed-off-by: Rob Herring (Arm) <robh@kernel.org>
Link: https://patch.msgid.link/20240826191728.1415189-1-robh@kernel.org
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>