gpio: ftgpio: Fix an error handling path in 'ftgpio_gpio_probe()'

If 'devm_kcalloc()' fails, we should go through the error handling path,
should some clean-up be needed.

Fixes: 42d9fc71 ("gpio: ftgpio: Pass irqchip when adding gpiochip")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/20190822204538.4791-1-christophe.jaillet@wanadoo.fr


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>