gpio: spear-spics: remove platform_set_drvdata() + cleanup probe

gpio: spear-spics: remove platform_set_drvdata() + cleanup probe

The platform_set_drvdata() call is only useful if we need to retrieve back
the private information.
Since the driver doesn't do that, it's not useful to have it.

If this is removed, we can also just do a direct return on
devm_gpiochip_add_data(). We don't need to print that this call failed as
there are other ways to log/see this during probe.

This change isn't removing the 'DT probe failed' message, as some may find
it useful as a reason for the failed probe. But that can be part of another
change if needed.

Signed-off-by: Alexandru Ardelean <aardelean@deviqon.com>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>