core: ofnode: do not assert if node not valid in ofnode_get_name()

In some case with LIVE DT, some node always not valid, or not have
a valid name, eg. blk driver add by mmc.
Return fail instead of Assert for this kind of ofnode, and this
help with assert happen from time to time when of_live is enabled
and DEBUG is enabled.

Signed-off-by: Kever Yang <kever.yang@rock-chips.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/core/ofnode.c b/drivers/core/ofnode.c
index 2ac73af..e74a662 100644
--- a/drivers/core/ofnode.c
+++ b/drivers/core/ofnode.c
@@ -212,7 +212,11 @@
 
 const char *ofnode_get_name(ofnode node)
 {
-	assert(ofnode_valid(node));
+	if (!ofnode_valid(node)) {
+		debug("%s node not valid\n", __func__);
+		return NULL;
+	}
+
 	if (ofnode_is_np(node))
 		return strrchr(node.np->full_name, '/') + 1;