mmc: rockchip: Log some error returns

Add a little logging to some places in this driver, to aid debugging
when something goes wrong.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/mmc/rockchip_dw_mmc.c b/drivers/mmc/rockchip_dw_mmc.c
index fb77b04..7e34166 100644
--- a/drivers/mmc/rockchip_dw_mmc.c
+++ b/drivers/mmc/rockchip_dw_mmc.c
@@ -80,7 +80,7 @@
 	priv->fifo_depth = dev_read_u32_default(dev, "fifo-depth", 0);
 
 	if (priv->fifo_depth < 0)
-		return -EINVAL;
+		return log_msg_ret("rkp", -EINVAL);
 	priv->fifo_mode = dev_read_bool(dev, "fifo-mode");
 
 #ifdef CONFIG_SPL_BUILD
@@ -96,7 +96,7 @@
 		int val = dev_read_u32_default(dev, "max-frequency", -EINVAL);
 
 		if (val < 0)
-			return val;
+			return log_msg_ret("rkc", val);
 
 		priv->minmax[0] = 400000;  /* 400 kHz */
 		priv->minmax[1] = val;