pinctrl: remove redundant mux_setting clear in pinmux_disable_setting()

desc->mux_setting is set to NULL in pin_free() called just below.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/pinctrl/pinmux.c

@@ -493,8 +493,6 @@ void pinmux_disable_setting(const struct pinctrl_setting *setting)
 			continue;
 		}
 		if (desc->mux_setting == &(setting->data.mux)) {
-			desc->mux_setting = NULL;
-			/* And release the pin */
 			pin_free(pctldev, pins[i], NULL);
 		} else {
 			const char *gname;