pinctrl: tz1090-pinctrl.txt: Fix typo in binding

Fix a typo, s/which which/which/ in the img,tz1090-pinctrl.txt binding.

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: linux-gpio@vger.kernel.org
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>