gpio: dwapb_gpio: fix broken dev->node

commit 1b898ffc ("gpio: dwapb_gpio: convert to livetree") introduced
a bug in that dev->node of the gpio chip was accidentally set to the
of_node of its bank subnode.

What it meant to do was assign subdev->node, not dev->node.

While this doesn't affect too many use cases, iterating over the gpio
chip's properties doesn't work any more after that, so fix this.

Fixes: commit 1b898ffc ("gpio: dwapb_gpio: convert to livetree")
Signed-off-by: Simon Goldschmidt <simon.k.r.goldschmidt@gmail.com>