gpio: vf610: Use PTR_ERR_OR_ZERO() in vf610_gpio_probe()

Simplify error checking code by replacing multiple ERR macros with a
call to PTR_ERR_OR_ZERO. No functional change intended.

Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Cc: Chris Healy <cphealy@gmail.com>
Cc: linux-gpio@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Reviewed-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>