dt-bindings: gpio: pca953x: Increase allowed length for gpio-line-names

Some supported chips (e.g. pca9505) support 40 lines. To be able to give
each line a name the length of the gpio-line-names property must be
allowed to contain up to 40 entries.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>