gpio: xgene: remove redundant error message

There's no need to emit an error message on probe failure unless we're
printing some meaningful info. Otherwise the core driver code will
inform us about a probe error.

Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>