tracing: Fix a NULL vs IS_ERR() bug in event_subsystem_dir()

The eventfs_create_dir() function returns error pointers, it never returns
NULL.  Update the check to reflect that.

Link: https://lore.kernel.org/linux-trace-kernel/ff641474-84e2-46a7-9d7a-62b251a1050c@moroto.mountain

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Fixes: 5790b1f ("eventfs: Remove eventfs_file and just use eventfs_inode")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

Author: Dan Carpenter

kernel/trace/trace_events.c

@@ -2354,7 +2354,7 @@ event_subsystem_dir(struct trace_array *tr, const char *name,
 		nr_entries = ARRAY_SIZE(system_entries);
 
 	ei = eventfs_create_dir(name, parent, system_entries, nr_entries, dir);
-	if (!ei) {
+	if (IS_ERR(ei)) {
 		pr_warn("Failed to create system directory %s\n", name);
 		__put_system(system);
 		goto out_free;