[TIPC]: Fix simple sparse warnings

Tried to run the new tipc stack through sparse.
Following patch fixes all cases where 0 was used
as replacement of NULL.
Use NULL to document this is a pointer and to silence sparse.

This brough sparse warning count down with 127 to 24 warnings.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Per Liden <per.liden@ericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/tipc/cluster.c b/net/tipc/cluster.c
index ab974ca..9fe45a4 100644
--- a/net/tipc/cluster.c
+++ b/net/tipc/cluster.c
@@ -48,7 +48,7 @@
 			 u32 lower, u32 upper);
 struct sk_buff *tipc_cltr_prepare_routing_msg(u32 data_size, u32 dest);
 
-struct node **tipc_local_nodes = 0;
+struct node **tipc_local_nodes = NULL;
 struct node_map tipc_cltr_bcast_nodes = {0,{0,}};
 u32 tipc_highest_allowed_slave = 0;
 
@@ -61,7 +61,7 @@
 
 	c_ptr = (struct cluster *)kmalloc(sizeof(*c_ptr), GFP_ATOMIC);
 	if (c_ptr == NULL)
-		return 0;
+		return NULL;
 	memset(c_ptr, 0, sizeof(*c_ptr));
 
 	c_ptr->addr = tipc_addr(tipc_zone(addr), tipc_cluster(addr), 0);
@@ -73,7 +73,7 @@
 	c_ptr->nodes = (struct node **)kmalloc(alloc, GFP_ATOMIC);
 	if (c_ptr->nodes == NULL) {
 		kfree(c_ptr);
-		return 0;
+		return NULL;
 	}
 	memset(c_ptr->nodes, 0, alloc);  
 	if (in_own_cluster(addr))
@@ -91,7 +91,7 @@
 	}
 	else {
 		kfree(c_ptr);
-		c_ptr = 0;
+		c_ptr = NULL;
 	}
 
 	return c_ptr;
@@ -204,7 +204,7 @@
 
 	assert(!in_own_cluster(c_ptr->addr));
 	if (!c_ptr->highest_node)
-		return 0;
+		return NULL;
 
 	/* Start entry must be random */
 	while (mask > c_ptr->highest_node) {
@@ -222,7 +222,7 @@
 		if (tipc_node_has_active_links(c_ptr->nodes[n_num]))
 			return c_ptr->nodes[n_num];
 	}
-	return 0;
+	return NULL;
 }
 
 /*