gpio: shared: ignore special __symbols__ node when traversing device tree

gpio: shared: ignore special __symbols__ node when traversing device tree

The __symbols__ node is a special, internal node and its properties must
not be considered when scanning the device-tree for shared GPIOs.

Fixes: a060b8c511ab ("gpiolib: implement low-level, shared GPIO support")
Reported-by: Jon Hunter <jonathanh@nvidia.com>
Closes: https://lore.kernel.org/all/0829a21c-f97d-41b6-90bc-2acaec42caab@nvidia.com/
Tested-by: Jon Hunter <jonathanh@nvidia.com>
Acked-by: Jon Hunter <jonathanh@nvidia.com>
Link: https://lore.kernel.org/r/20251126-gpio-shared-fixes-v1-1-18309c0e87b5@linaro.org
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>