clk: gpio: Mark parent_names array const

Let's encourage const arrays of parent names like other basic
clock types.

Cc: Sergej Sawazki <ce3a@gmx.de>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
diff --git a/include/linux/clk-provider.h b/include/linux/clk-provider.h
index 699a250..06a56e5 100644
--- a/include/linux/clk-provider.h
+++ b/include/linux/clk-provider.h
@@ -583,7 +583,7 @@
 
 extern const struct clk_ops clk_gpio_mux_ops;
 struct clk *clk_register_gpio_mux(struct device *dev, const char *name,
-		const char **parent_names, u8 num_parents, unsigned gpio,
+		const char * const *parent_names, u8 num_parents, unsigned gpio,
 		bool active_low, unsigned long flags);
 
 void of_gpio_mux_clk_setup(struct device_node *node);