qup_i2c: set up node before calling of_i2c_register_devices

Device-tree framework for I2C expects adapter of device's
of_node to be initialized before adding I2C slave devices
on the bus.

Change-Id: I64af0b6bafb71ec94ad5acfe3034e9be887ebc47
Signed-off-by: Amy Maloche <amaloche@codeaurora.org>