gpio: viperboard: remove platform_set_drvdata() call in 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.

This change removes it.
Also removing with this change is some logging about the failure to init
the gpio chip data. There are other logging methods to view that this
failed.

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