clk: Return -ENOSYS when system call is not available

Update clk_composite_set_parent() to use -ENOSYS, which is the correct
error code for U-Boot. Also rearrange the code so that the error condition
is clearly indicated and the function runs to the end in the normal case,
since this is the common style in U-Boot.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Sean Anderson <seanga2@gmail.com>

drivers/clk/clk-composite.c

@@ -37,10 +37,10 @@ static int clk_composite_set_parent(struct clk *clk, struct clk *parent)
 	const struct clk_ops *mux_ops = composite->mux_ops;
 	struct clk *mux = composite->mux;
 
-	if (mux && mux_ops)
-		return mux_ops->set_parent(mux, parent);
-	else
-		return -ENOTSUPP;
+	if (!mux || !mux_ops)
+		return -ENOSYS;
+
+	return mux_ops->set_parent(mux, parent);
 }
 
 static unsigned long clk_composite_recalc_rate(struct clk *clk)