clk: handle NULL struct clk gracefully

At some point changes to clk_set_rate and clk_set_parent introduced a
bug whereby NULL struct clk pointers were treated as an error. This is
in violation of the API in include/linux/clk.h. Reintroduce graceful
handling of NULL clk's by bailing from clk_set_rate and clk_set_parent
with return codes of zero.

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

drivers/clk/clk.c

@@ -1428,6 +1428,9 @@ int clk_set_rate(struct clk *clk, unsigned long rate)
 	struct clk *top, *fail_clk;
 	int ret = 0;
 
+	if (!clk)
+		return 0;
+
 	/* prevent racing with updates to the clock topology */
 	clk_prepare_lock();
 
@@ -1567,7 +1570,10 @@ int clk_set_parent(struct clk *clk, struct clk *parent)
 	u8 p_index = 0;
 	unsigned long p_rate = 0;
 
-	if (!clk || !clk->ops)
+	if (!clk)
+		return 0;
+
+	if (!clk->ops)
 		return -EINVAL;
 
 	/* verify ops for for multi-parent clks */