pinctrl: remove maxpin from documentation

struct pinctrl_desc does not contain the maxpin member since commit 0d2006bb
(pinctrl: remove unnecessary max pin number).

Fixes: 0d2006bb ('pinctrl: remove unnecessary max pin number')
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

Documentation/pinctrl.txt

@@ -72,7 +72,6 @@ static struct pinctrl_desc foo_desc = {
 	.name = "foo",
 	.pins = foo_pins,
 	.npins = ARRAY_SIZE(foo_pins),
-	.maxpin = 63,
 	.owner = THIS_MODULE,
 };