gpiolib: acpi: use the fwnode in acpi_gpiochip_find()

While trying to set up an SSDT override for a USB-2-I2C chip [0],
I realized that the function acpi_gpiochip_find() was using the parent
of the gpio_chip to do the ACPI matching.

This works fine on my Ice Lake laptop because AFAICT, the DSDT presents
the PCI device INT3455 as the "Device (GPI0)", but is in fact handled
by the pinctrl driver in Linux.
The pinctrl driver then creates a gpio_chip device. This means that the
gc->parent device in that case is the GPI0 device from ACPI and everything
works.

However, in the hid-cp2112 case, the parent is the USB device, and the
gpio_chip is directly under that USB device. Which means that in this case
gc->parent points at the USB device, and so we can not do an ACPI match
towards the GPIO device.

I think it is safe to resolve the ACPI matching through the fwnode
because when we call gpiochip_add_data(), the first thing it does is
setting a proper gc->fwnode: if it is not there, it borrows the fwnode
of the parent.

So in my Ice Lake case, gc->fwnode is the one from the parent, meaning
that the ACPI handle we will get is the one from the GPI0 in the DSDT
(the pincrtl one). And in the hid-cp2112 case, we get the actual
fwnode from the gpiochip we created in the HID device, making it working.

Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Link: https://lore.kernel.org/linux-input/20230227140758.1575-1-kaehndan@gmail.com/T/#m592f18081ef3b95b618694a612ff864420c5aaf3 [0]
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>