i2c: dln2: set the device tree node of the adapter

This patch makes sure the platform device tree node is inherited by
the adapter device. This allows the DLN2 bus to work with i2c devices
defined in the device tree.

Signed-off-by: Octavian Purdila <octavian.purdila@intel.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>