libfdt: overlay: Check the value of the right variable

overlay_update_local_node_references() saves the result of
fdt_subnode_offset() into variable tree_child but checks for variable
ret afterwards. As this does not make sense, check tree_child instead of
ret.

This bug has been found by compiling with clang. The compiler reported
the following warning:

    libfdt/fdt_overlay.c:275:7: error: variable 'ret' may be
    uninitialized when used here
          [-Werror,-Wconditional-uninitialized]
                    if (ret == -FDT_ERR_NOTFOUND)
                        ^~~
    libfdt/fdt_overlay.c:210:9: note: initialize the variable 'ret' to
    silence this
          warning
            int ret;
                   ^
                    = 0

Signed-off-by: Nicolas Iooss <nicolas.iooss_linux@m4x.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
diff --git a/libfdt/fdt_overlay.c b/libfdt/fdt_overlay.c
index 9d03221..ceb9687 100644
--- a/libfdt/fdt_overlay.c
+++ b/libfdt/fdt_overlay.c
@@ -271,7 +271,7 @@
 
 		tree_child = fdt_subnode_offset(fdto, tree_node,
 						fixup_child_name);
-		if (ret == -FDT_ERR_NOTFOUND)
+		if (tree_child == -FDT_ERR_NOTFOUND)
 			return -FDT_ERR_BADOVERLAY;
 		if (tree_child < 0)
 			return tree_child;