mux: constify mux class

All class functions used here take a const pointer to the class
structure so we can make the struct itself constant.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Signed-off-by: Peter Rosin <peda@axentia.se>

drivers/mux/core.c

@@ -42,7 +42,7 @@ struct mux_state {
 	unsigned int state;
 };
 
-static struct class mux_class = {
+static const struct class mux_class = {
 	.name = "mux",
 };