cmd: jffs2: use get_nand_dev_by_index()

As part of preparation for nand DM conversion the new API has been
introduced to remove direct access to nand_info array. So, use it here
instead of accessing to nand_info array directly.

Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
diff --git a/cmd/jffs2.c b/cmd/jffs2.c
index 9be198e..dc94705 100644
--- a/cmd/jffs2.c
+++ b/cmd/jffs2.c
@@ -166,8 +166,9 @@
 #endif
 	} else if (type == MTD_DEV_TYPE_NAND) {
 #if defined(CONFIG_JFFS2_NAND) && defined(CONFIG_CMD_NAND)
-		if (num < CONFIG_SYS_MAX_NAND_DEVICE) {
-			*size = nand_info[num]->size;
+		struct mtd_info *mtd = get_nand_dev_by_index(num);
+		if (mtd) {
+			*size = mtd->size;
 			return 0;
 		}
 
@@ -244,7 +245,7 @@
 #if defined(CONFIG_JFFS2_NAND) && defined(CONFIG_CMD_NAND)
 	struct mtd_info *mtd;
 
-	mtd = nand_info[id->num];
+	mtd = get_nand_dev_by_index(id->num);
 
 	return mtd->erasesize;
 #else