clk: Rename clk_get_by_driver_info()

This is actually a misnomer now, since the phandle info may contain
a driver_info index or a udevice index. Rename it to use the word
'phandle', which seems more accurate. Add a comment while we are here.

Also add a test for this function.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/ram/rockchip/sdram_rk3399.c b/drivers/ram/rockchip/sdram_rk3399.c
index ce33fbb..c0a06dc 100644
--- a/drivers/ram/rockchip/sdram_rk3399.c
+++ b/drivers/ram/rockchip/sdram_rk3399.c
@@ -3107,7 +3107,7 @@
 	      priv->cic, priv->pmugrf, priv->pmusgrf, priv->pmucru, priv->pmu);
 
 #if CONFIG_IS_ENABLED(OF_PLATDATA)
-	ret = clk_get_by_driver_info(dev, dtplat->clocks, &priv->ddr_clk);
+	ret = clk_get_by_phandle(dev, dtplat->clocks, &priv->ddr_clk);
 #else
 	ret = clk_get_by_index(dev, 0, &priv->ddr_clk);
 #endif