of/i2c: Fill the archdata for I2C devices

For I2C devices we just setting the node pointer in the archdata. This
is needed so that the I2C devices could find their OF tree nodes.

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Acked-by: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: Paul Mackerras <paulus@samba.org>