regulator: lp872x: use the private data instead of updating I2C device platform data

Currently, lp872x driver parses the DT and copies values into the
'cl->dev.platform_data' if 'of_node' exists.
This may have architectural issue. Platform data is configurable through
the DT or I2C board info inside the platform area.
However, lp872x driver changes this configuration when it is loaded.

The lp872x driver should get data from the platform side and use the private
data, 'lp872x->pdata' instead of changing the original platform data.

Signed-off-by: Milo Kim <milo.kim@ti.com>
Signed-off-by: Mark Brown <broonie@kernel.org>