pinctrl: pistachio: Correct the fwnode_irq_get() return value check

fwnode_irq_get() may return all possible signed values, such as Linux
error code or 0. Fix the code to handle this properly.

Fixes: 1074e1d2 ("pinctrl: pistachio: Switch to use fwnode instead of")
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20220908094323.31965-1-andriy.shevchenko@linux.intel.com


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