extcon: int3496: Propagate error code of gpiod_to_irq()

gpiod_to_irq() doesn't return 0. Thus, we just adjust condition and
replace -EINVAL by actual error code it returns.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>