The lp8788-adc is a platform driver of lp8788-mfd.
The platform device is allocated when mfd_add_devices() is called
in lp8788-mfd.
On the other hand, 'lp->dev' is the i2c client device.
Therefore, this 'platform_device' is a proper parent device of
iio device and device kernel message.
Signed-off-by: Milo(Woogyom) Kim <milo.kim@ti.com> Signed-off-by: Jonathan Cameron <jic23@kernel.org>