ram: sifive: Check return value on clk_enable()

The return value should be checked otherwise it's useless to
assign the return value to 'ret'.

Signed-off-by: Bin Meng <bin.meng@windriver.com>
diff --git a/drivers/ram/sifive/fu540_ddr.c b/drivers/ram/sifive/fu540_ddr.c
index 5ff8869..f5b2873 100644
--- a/drivers/ram/sifive/fu540_ddr.c
+++ b/drivers/ram/sifive/fu540_ddr.c
@@ -369,6 +369,11 @@
 	}
 
 	ret = clk_enable(&priv->ddr_clk);
+	if (ret < 0) {
+		debug("Could not enable DDR clock\n");
+		return ret;
+	}
+
 	priv->ctl = regmap_get_range(map, 0);
 	priv->phy = regmap_get_range(map, 1);
 	priv->physical_filter_ctrl = regmap_get_range(map, 2);