docs/pinctrl: fix runtime pinmuxing example

The example declares "struct pinctrl *p" but refers to
"foo->p" which isn't declared in the context of the example.
Signed-off-by: Siarhei Volkau <lis8215@gmail.com>
Link: https://lore.kernel.org/r/20221101205159.1468069-3-lis8215@gmail.comSigned-off-by: Linus Walleij <linus.walleij@linaro.org>

Documentation/driver-api/pin-control.rst

@@ -1399,11 +1399,11 @@ on the pins defined by group B::
 		if (IS_ERR(p))
 			...
 
-		s1 = pinctrl_lookup_state(foo->p, "pos-A");
+		s1 = pinctrl_lookup_state(p, "pos-A");
 		if (IS_ERR(s1))
 			...
 
-		s2 = pinctrl_lookup_state(foo->p, "pos-B");
+		s2 = pinctrl_lookup_state(p, "pos-B");
 		if (IS_ERR(s2))
 			...
 	}