clk: add clk_round_rate()

It returns the rate which will be set if you ask clk_set_rate() to set
that rate. It provides a way to query exactly what rate you'll get if
you call clk_set_rate() with that same argument.
So essentially, clk_round_rate() and clk_set_rate() are equivalent
except the former does not modify the clock hardware in any way.

Signed-off-by: Dario Binacchi <dariobin@libero.it>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Sean Anderson <seanga2@gmail.com>
diff --git a/drivers/clk/clk_sandbox_test.c b/drivers/clk/clk_sandbox_test.c
index e9eb738..c4e4481 100644
--- a/drivers/clk/clk_sandbox_test.c
+++ b/drivers/clk/clk_sandbox_test.c
@@ -86,6 +86,16 @@
 	return clk_get_rate(sbct->clkps[id]);
 }
 
+ulong sandbox_clk_test_round_rate(struct udevice *dev, int id, ulong rate)
+{
+	struct sandbox_clk_test *sbct = dev_get_priv(dev);
+
+	if (id < 0 || id >= SANDBOX_CLK_TEST_ID_COUNT)
+		return -EINVAL;
+
+	return clk_round_rate(sbct->clkps[id], rate);
+}
+
 ulong sandbox_clk_test_set_rate(struct udevice *dev, int id, ulong rate)
 {
 	struct sandbox_clk_test *sbct = dev_get_priv(dev);