tracing: checking for NULL instead of IS_ERR()

tracing_map_elt_alloc() returns ERR_PTRs on error, never NULL.

Fixes: 08d43a5fa063 ('tracing: Add lock-free tracing_map')
Link: http://lkml.kernel.org/r/20160423102347.GA11136@mwanda

Acked-by: Tom Zanussi <tom.zanussi@linux.intel.com>
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

kernel/trace/tracing_map.c

@@ -814,7 +814,7 @@ static struct tracing_map_elt *copy_elt(struct tracing_map_elt *elt)
 	unsigned int i;
 
 	dup_elt = tracing_map_elt_alloc(elt->map);
-	if (!dup_elt)
+	if (IS_ERR(dup_elt))
 		return NULL;
 
 	if (elt->map->ops && elt->map->ops->elt_copy)