mtd: Create gluebi mtdblocks if CONFIG_FTL is not enabled

Upstream commit
a43bdc3 ("mtd: Fix gluebi NULL pointer dereference caused by ftl notifier")
fixed a NULL pointer dereference, which can be caused by FTL notifier
accessing 'gluebi->desc' in gluebi_read, by completely preventing gluebi
from creating mtdblock devices.

This creates a problem as existing systems may expect mtdblocks emulated
on top of UBI to exist. As a workaround, this commit prevents gluebi
mtdblock device creation only if CONFIG_FTL is enabled.

Signed-off-by: HatsyRei <yan.huan.chng@emerson.com>
[gratian: reword to match commit quoting kernel standard]
Signed-off-by: Gratian Crisan <gratian.crisan@emerson.com>

Author: HatsyRei

drivers/mtd/mtd_blkdevs.c

@@ -463,7 +463,8 @@ static void blktrans_notify_add(struct mtd_info *mtd)
 {
 	struct mtd_blktrans_ops *tr;
 
-	if (mtd->type == MTD_ABSENT || mtd->type == MTD_UBIVOLUME)
+	if (mtd->type == MTD_ABSENT ||
+	   (IS_ENABLED(CONFIG_FTL) && mtd->type == MTD_UBIVOLUME))
 		return;
 
 	list_for_each_entry(tr, &blktrans_majors, list)
@@ -503,7 +504,8 @@ int register_mtd_blktrans(struct mtd_blktrans_ops *tr)
 	mutex_lock(&mtd_table_mutex);
 	list_add(&tr->list, &blktrans_majors);
 	mtd_for_each_device(mtd)
-		if (mtd->type != MTD_ABSENT && mtd->type != MTD_UBIVOLUME)
+		if (mtd->type != MTD_ABSENT &&
+		   !(IS_ENABLED(CONFIG_FTL) && mtd->type == MTD_UBIVOLUME))
 			tr->add_mtd(tr, mtd);
 	mutex_unlock(&mtd_table_mutex);
 	return 0;