UBIFS: fix debugfs-less systems support

Commit "f70b7e5 UBIFS: remove Kconfig debugging option" broke UBIFS and it
refuses to initialize if debugfs (CONFIG_DEBUG_FS) is disabled. I incorrectly
assumed that debugfs files creation function will return success if debugfs
is disabled, but they actually return -ENODEV. This patch fixes the issue.

Reported-by: Paul Parsons <lost.distance@yahoo.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Tested-by: Paul Parsons <lost.distance@yahoo.com>

fs/ubifs/debug.c

@@ -2918,6 +2918,9 @@ int dbg_debugfs_init_fs(struct ubifs_info *c)
 	struct dentry *dent;
 	struct ubifs_debug_info *d = c->dbg;
 
+	if (!IS_ENABLED(DEBUG_FS))
+		return 0;
+
 	n = snprintf(d->dfs_dir_name, UBIFS_DFS_DIR_LEN + 1, UBIFS_DFS_DIR_NAME,
 		     c->vi.ubi_num, c->vi.vol_id);
 	if (n == UBIFS_DFS_DIR_LEN) {
@@ -3010,7 +3013,8 @@ out:
  */
 void dbg_debugfs_exit_fs(struct ubifs_info *c)
 {
-	debugfs_remove_recursive(c->dbg->dfs_dir);
+	if (IS_ENABLED(DEBUG_FS))
+		debugfs_remove_recursive(c->dbg->dfs_dir);
 }
 
 struct ubifs_global_debug_info ubifs_dbg;
@@ -3095,6 +3099,9 @@ int dbg_debugfs_init(void)
 	const char *fname;
 	struct dentry *dent;
 
+	if (!IS_ENABLED(DEBUG_FS))
+		return 0;
+
 	fname = "ubifs";
 	dent = debugfs_create_dir(fname, NULL);
 	if (IS_ERR_OR_NULL(dent))
@@ -3159,7 +3166,8 @@ out:
  */
 void dbg_debugfs_exit(void)
 {
-	debugfs_remove_recursive(dfs_rootdir);
+	if (IS_ENABLED(DEBUG_FS))
+		debugfs_remove_recursive(dfs_rootdir);
 }
 
 /**