backing-dev: no need to check return value of debugfs_create functions

When calling debugfs functions, there is no need to ever check the
return value.  The function can work or not, but the code logic should
never do something different based on this.

And as the return value does not matter at all, no need to save the
dentry in struct backing_dev_info, so delete it.

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Anders Roxell <anders.roxell@linaro.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Michal Hocko <mhocko@suse.com>
Cc: linux-mm@kvack.org
Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

include/linux/backing-dev-defs.h

@@ -203,7 +203,6 @@ struct backing_dev_info {
 
 #ifdef CONFIG_DEBUG_FS
 	struct dentry *debug_dir;
-	struct dentry *debug_stats;
 #endif
 };
 

mm/backing-dev.c

@@ -103,39 +103,25 @@ static int bdi_debug_stats_show(struct seq_file *m, void *v)
 }
 DEFINE_SHOW_ATTRIBUTE(bdi_debug_stats);
 
-static int bdi_debug_register(struct backing_dev_info *bdi, const char *name)
+static void bdi_debug_register(struct backing_dev_info *bdi, const char *name)
 {
-	if (!bdi_debug_root)
-		return -ENOMEM;
-
 	bdi->debug_dir = debugfs_create_dir(name, bdi_debug_root);
-	if (!bdi->debug_dir)
-		return -ENOMEM;
 
-	bdi->debug_stats = debugfs_create_file("stats", 0444, bdi->debug_dir,
-					       bdi, &bdi_debug_stats_fops);
-	if (!bdi->debug_stats) {
-		debugfs_remove(bdi->debug_dir);
-		bdi->debug_dir = NULL;
-		return -ENOMEM;
-	}
-
-	return 0;
+	debugfs_create_file("stats", 0444, bdi->debug_dir, bdi,
+			    &bdi_debug_stats_fops);
 }
 
 static void bdi_debug_unregister(struct backing_dev_info *bdi)
 {
-	debugfs_remove(bdi->debug_stats);
-	debugfs_remove(bdi->debug_dir);
+	debugfs_remove_recursive(bdi->debug_dir);
 }
 #else
 static inline void bdi_debug_init(void)
 {
 }
-static inline int bdi_debug_register(struct backing_dev_info *bdi,
+static inline void bdi_debug_register(struct backing_dev_info *bdi,
 				      const char *name)
 {
-	return 0;
 }
 static inline void bdi_debug_unregister(struct backing_dev_info *bdi)
 {