fwnode_irq_get() can return zero to indicate IRQ mapping errors.
Handle this case by skipping the interrupt resource.

Fixes: a1d1e0e3 ("pinctrl: nuvoton: Add driver for WPCM450")
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Link: https://lore.kernel.org/r/20220927175509.15695-1-andriy.shevchenko@linux.intel.comSigned-off-by: Linus Walleij <linus.walleij@linaro.org>