clk: core: copy parent_names & return error codes

This patch cleans up clk_register and solves a few bugs by teaching
clk_register and __clk_init to return error codes (instead of just NULL)
to better align with the existing clk.h api.

Along with that change this patch also introduces a new behavior whereby
clk_register copies the parent_names array, thus allowing platforms to
declare their parent_names arrays as __initdata.

Signed-off-by: Mike Turquette <mturquette@linaro.org>

include/linux/clk-private.h

@@ -181,8 +181,10 @@ struct clk {
  *
  * It is not necessary to call clk_register if __clk_init is used directly with
  * statically initialized clock data.
+ *
+ * Returns 0 on success, otherwise an error code.
  */
-void __clk_init(struct device *dev, struct clk *clk);
+int __clk_init(struct device *dev, struct clk *clk);
 
 #endif /* CONFIG_COMMON_CLK */
 #endif /* CLK_PRIVATE_H */