gpio: sim: pass the GPIO device's software node to irq domain

[ Upstream commit 6e39c1ac ]

Associate the swnode of the GPIO device's (which is the interrupt
controller here) with the irq domain. Otherwise the interrupt-controller
device attribute is a no-op.

Fixes: cb8c474e ("gpio: sim: new testing module")
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>