USB: mon: Allow to use usbmon without debugfs

Do not bail out with an error in mon_text_init() if debugfs is not
available, instead just return 0 and let mon_init() go ahead with
loading the binary API. Return -ENOMEM in case debugfs_create_dir()
fails for other reasons. Later, it is enough to check for mon_dir
not set.

Signed-off-by: Tobias Klauser <[e-mail]>
Signed-off-by: Pete Zaitcev <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/usb/mon/mon_text.c

···
 	int busnum = ubus? ubus->busnum: 0;
 	int rc;
 
+	if (mon_dir == NULL)
+		return 0;
+
 	if (ubus != NULL) {
 		rc = snprintf(name, NAMESZ, "%dt", busnum);
 		if (rc <= 0 || rc >= NAMESZ)
···
 
 	mondir = debugfs_create_dir("usbmon", usb_debug_root);
 	if (IS_ERR(mondir)) {
-		printk(KERN_NOTICE TAG ": debugfs is not available\n");
-		return -ENODEV;
+		/* debugfs not available, but we can use usbmon without it */
+		return 0;
 	}
 	if (mondir == NULL) {
 		printk(KERN_NOTICE TAG ": unable to create usbmon directory\n");
-		return -ENODEV;
+		return -ENOMEM;
 	}
 	mon_dir = mondir;
 	return 0;