UBI: correct usage of IS_ENABLED()

Commit "e9b4cf2 UBI: fix debugfs-less systems support" fixed one
regression but introduced a different regression - the debugfs is now always
compiled out. Root cause: IS_ENABLED() arguments should be used with the
CONFIG_* prefix.

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>

drivers/mtd/ubi/debug.c

@@ -264,7 +264,7 @@ static struct dentry *dfs_rootdir;
  */
 int ubi_debugfs_init(void)
 {
-	if (!IS_ENABLED(DEBUG_FS))
+	if (!IS_ENABLED(CONFIG_DEBUG_FS))
 		return 0;
 
 	dfs_rootdir = debugfs_create_dir("ubi", NULL);
@@ -284,7 +284,7 @@ int ubi_debugfs_init(void)
  */
 void ubi_debugfs_exit(void)
 {
-	if (IS_ENABLED(DEBUG_FS))
+	if (IS_ENABLED(CONFIG_DEBUG_FS))
 		debugfs_remove(dfs_rootdir);
 }
 
@@ -407,7 +407,7 @@ int ubi_debugfs_init_dev(struct ubi_device *ubi)
 	struct dentry *dent;
 	struct ubi_debug_info *d = ubi->dbg;
 
-	if (!IS_ENABLED(DEBUG_FS))
+	if (!IS_ENABLED(CONFIG_DEBUG_FS))
 		return 0;
 
 	n = snprintf(d->dfs_dir_name, UBI_DFS_DIR_LEN + 1, UBI_DFS_DIR_NAME,
@@ -477,6 +477,6 @@ out:
  */
 void ubi_debugfs_exit_dev(struct ubi_device *ubi)
 {
-	if (IS_ENABLED(DEBUG_FS))
+	if (IS_ENABLED(CONFIG_DEBUG_FS))
 		debugfs_remove_recursive(ubi->dbg->dfs_dir);
 }