pinctrl: bcm2835: Handle gpiochip_add_pin_range() errors

gpiochip_add_pin_range() can fail, so better return its error code than
a hard coded '0'.

Fixes: d2b67744

 ("pinctrl: bcm2835: implement hook for missing gpio-ranges")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/98c3b5890bb72415145c9fe4e1d974711edae376.1681681402.git.christophe.jaillet@wanadoo.fr
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>