gpio: pca953x: Swap if statements to save later complexity

A later patch in the series adds support for a further chip type that
shares some similarity with the PCA953X_TYPE. In order to keep the logic
simple, swap over the if and else portions where checks are made against
PCA953X_TYPE and instead check for PCA957X_TYPE.

Signed-off-by: Martyn Welch <martyn.welch@collabora.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>