docs/pinctrl: fix compile errors in example code

The code in the example does not build for a few trivial errors: type
mismatch in callback, missing semicolon. Fix them to help newcomers using
the example as a starting point.
Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
Link: https://lore.kernel.org/r/20190705143043.1929-1-luca@lucaceresoli.netSigned-off-by: Linus Walleij <linus.walleij@linaro.org>

Documentation/driver-api/pinctl.rst

@@ -638,8 +638,8 @@ group of pins would work something like this::
 	}
 
 	static int foo_get_group_pins(struct pinctrl_dev *pctldev, unsigned selector,
-				unsigned ** const pins,
-				unsigned * const num_pins)
+				const unsigned ** pins,
+				unsigned * num_pins)
 	{
 		*pins = (unsigned *) foo_groups[selector].pins;
 		*num_pins = foo_groups[selector].num_pins;
@@ -705,7 +705,7 @@ group of pins would work something like this::
 	{
 		u8 regbit = (1 << selector + group);
 
-		writeb((readb(MUX)|regbit), MUX)
+		writeb((readb(MUX)|regbit), MUX);
 		return 0;
 	}