livetree: fix leak spotted by ASAN

./dtc -I dts -O dtb -o overlay_base_manual_symbols.test.dtb /home/elmarco/src/dtc/tests/overlay_base_manual_symbols.dts
../data.c:109:2: runtime error: null pointer passed as argument 2, which is declared to never be null

=================================================================
==933317==ERROR: LeakSanitizer: detected memory leaks

Direct leak of 24 byte(s) in 1 object(s) allocated from:
    #0 0x7f49a2aba6af in __interceptor_malloc (/lib64/libasan.so.8+0xba6af)
    #1 0x43183d in xmalloc ../util.h:45
    #2 0x43482f in data_add_marker ../data.c:230
    #3 0x449bb8 in get_node_phandle ../livetree.c:632
    #4 0x421058 in fixup_phandle_references ../checks.c:627
    #5 0x41b0ba in check_nodes_props ../checks.c:141
    #6 0x41b1c8 in check_nodes_props ../checks.c:144
    #7 0x41b9f1 in run_check ../checks.c:181
    #8 0x430a68 in process_checks ../checks.c:2057
    #9 0x436abd in main ../dtc.c:327
    #10 0x7f49a30d850f in __libc_start_call_main (/lib64/libc.so.6+0x2750f)

Only create data when necessary, and do not alias it.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
[dwg: Small fixup for a slightly different approach to adjacent cleanups]
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

livetree.c

@@ -617,10 +617,25 @@ struct node *get_node_by_ref(struct node *tree, const char *ref)
 	return target;
 }
 
+static void add_phandle_property(struct node *node,
+				 const char *name, int format)
+{
+	struct data d;
+
+	if (!(phandle_format & format))
+		return;
+	if (get_property(node, name))
+		return;
+
+	d = data_add_marker(empty_data, TYPE_UINT32, NULL);
+	d = data_append_cell(d, node->phandle);
+
+	add_property(node, build_property(name, d, NULL));
+}
+
 cell_t get_node_phandle(struct node *root, struct node *node)
 {
 	static cell_t phandle = 1; /* FIXME: ick, static local */
-	struct data d = empty_data;
 
 	if (phandle_is_valid(node->phandle))
 		return node->phandle;
@@ -630,16 +645,8 @@ cell_t get_node_phandle(struct node *root, struct node *node)
 
 	node->phandle = phandle;
 
-	d = data_add_marker(d, TYPE_UINT32, NULL);
-	d = data_append_cell(d, phandle);
-
-	if (!get_property(node, "linux,phandle")
-	    && (phandle_format & PHANDLE_LEGACY))
-		add_property(node, build_property("linux,phandle", d, NULL));
-
-	if (!get_property(node, "phandle")
-	    && (phandle_format & PHANDLE_EPAPR))
-		add_property(node, build_property("phandle", d, NULL));
+	add_phandle_property(node, "linux,phandle", PHANDLE_LEGACY);
+	add_phandle_property(node, "phandle", PHANDLE_EPAPR);
 
 	/* If the node *does* have a phandle property, we must
 	 * be dealing with a self-referencing phandle, which will be