pinctrl: core: Remove duplicated word from devm_pinctrl_unregister()

Remove duplicated "which" from devm_pinctrl_unregister() kernel doc
description.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Link: https://lore.kernel.org/r/8b75e5dfd9363f35ebdd7812e119757379678f97.1629877281.git.michal.simek@xilinx.com


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