dt-bindings: pinctrl: at91: Fix a typo ("descibe")

Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Link: https://lore.kernel.org/r/20200308214230.15193-1-j.neuschaefer@gmx.net


Acked-by: Ludovic Desroches <ludovic.desroches@microchip.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>