gpio: xgene: simplify probe, return devm_gpiochip_add_data() directly

The handling of the return value from devm_gpiochip_add_data() is a bit
redundant. It prints messages on error and success cases.
While the success message may be useful, it is more in the area of log
spam, and these can be printed with other forms of kernel logging.

This change does a direct return with devm_gpiochip_add_data() in the probe
function.

The platform_set_drvdata() is needed, as this driver uses the stored
private date in the PM suspend/resume routines.

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