pinctrl: remove useless const qualifier

This "const" claims the get_function_groups callback never
changes the given num_groups pointer.  It is always true
in C language, so not worth mentioning.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

include/linux/pinctrl/pinmux.h

@@ -69,7 +69,7 @@ struct pinmux_ops {
 	int (*get_function_groups) (struct pinctrl_dev *pctldev,
 				  unsigned selector,
 				  const char * const **groups,
-				  unsigned * const num_groups);
+				  unsigned *num_groups);
 	int (*set_mux) (struct pinctrl_dev *pctldev, unsigned func_selector,
 			unsigned group_selector);
 	int (*gpio_request_enable) (struct pinctrl_dev *pctldev,