gpio: pca953x: reduce indentation level in pca953x_irq_setup()

gpio: pca953x: reduce indentation level in pca953x_irq_setup()

The current design of pca953x_irq_setup() is:

 if (all conditions to support IRQ are met) {
   lots of code to support IRQs, which goes to a serious indentation
   level.
 }

 return 0;

It makes more sense to handle this like this:

 if (!all conditions to support IRQ are met)
   return 0;

 handle IRQ support

This commit does just this change, reducing by one tab the indentation
level of the IRQ setup code. Thanks to this reduced indentation level,
we are less restricted by the 80-column limit, and we can have more
function arguments on the same line.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>