clk: tegra: Fix build warnings on Tegra20/Tegra30

The recent conversion of proper const usage was only partial and didn't
include Tegra20 and Tegra30 support. Fix that up.

Signed-off-by: Thierry Reding <treding@nvidia.com>

drivers/clk/tegra/clk.h

@@ -590,7 +590,7 @@ struct clk *tegra_clk_register_periph(const char *name,
 		struct tegra_clk_periph *periph, void __iomem *clk_base,
 		u32 offset, unsigned long flags);
 struct clk *tegra_clk_register_periph_nodiv(const char *name,
-		const char **parent_names, int num_parents,
+		const char * const *parent_names, int num_parents,
 		struct tegra_clk_periph *periph, void __iomem *clk_base,
 		u32 offset);