gpio: htc-egpio: 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. Also: the driver currently drops info
about errors propagated from called functions by default to returning
-EINVAL. This fixes it as well.

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