gpio: pca953x: Request IRQ after all initialisation done

There is logically better to request IRQ when we initialise all structures.
Align the driver with the rest on the same matter.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20200728125504.27786-1-andriy.shevchenko@linux.intel.com


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