net: octeontx: smi: fix mii probe

The fdt node offset is apparently not set properly when probed
causing no MDIO busses to be found. Fix this by obtaining the
offset.

Signed-off-by: Tim Harvey <tharvey@gateworks.com>
Reviewed-by: Stefan Roese <sr@denx.de>
diff --git a/drivers/net/octeontx/smi.c b/drivers/net/octeontx/smi.c
index 91dcd05..27f4423 100644
--- a/drivers/net/octeontx/smi.c
+++ b/drivers/net/octeontx/smi.c
@@ -325,6 +325,8 @@
 		return -1;
 	}
 
+	node = fdt_node_offset_by_compatible(gd->fdt_blob, -1,
+					     "cavium,thunder-8890-mdio-nexus");
 	fdt_for_each_subnode(subnode, gd->fdt_blob, node) {
 		ret = fdt_node_check_compatible(gd->fdt_blob, subnode,
 						"cavium,thunder-8890-mdio");