mtd: nand: don't leak buffers when ->scan_bbt() fails

This bug seems to have been here forever, although we came close to
fixing all of them in [1]!

[1] 11eaf6df1c ("mtd: nand: Remove BUG() abuse in nand_scan_tail")

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Acked-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>

drivers/mtd/nand/nand_base.c

@@ -4842,7 +4842,11 @@ int nand_scan_tail(struct mtd_info *mtd)
 		return 0;
 
 	/* Build bad block table */
-	return chip->scan_bbt(mtd);
+	ret = chip->scan_bbt(mtd);
+	if (ret)
+		goto err_free;
+	return 0;
+
 err_free:
 	if (nbuf) {
 		kfree(nbuf->databuf);