nand: reinstate lazy bad block scanning

Commit ff94bc40af3481d47546595ba73c136de6af6929
("mtd, ubi, ubifs: resync with Linux-3.14")
accidentally reverted part of the commit
13f0fd94e3cae6f8a0d9fba5d367e311edc8ebde
("NAND: Scan bad blocks lazily.").

Reinstate the change as by commit
fb49454b1b6c7c6e238ac3c0b1e302e73eb1a1ea
("nand: reinstate lazy bad block scanning")

Signed-off-by: Rostislav Lisovy <lisovy@merica.cz>
Acked-by: Heiko Schocher <hs@denx.de>
diff --git a/drivers/mtd/nand/nand_base.c b/drivers/mtd/nand/nand_base.c
index 0b6e7ee..70e780c 100644
--- a/drivers/mtd/nand/nand_base.c
+++ b/drivers/mtd/nand/nand_base.c
@@ -634,6 +634,11 @@
 {
 	struct nand_chip *chip = mtd->priv;
 
+	if (!(chip->options & NAND_BBT_SCANNED)) {
+		chip->scan_bbt(mtd);
+		chip->options |= NAND_BBT_SCANNED;
+	}
+
 	if (!chip->bbt)
 		return chip->block_bad(mtd, ofs, getchip);
 
@@ -4322,10 +4327,9 @@
 
 	/* Check, if we should skip the bad block table scan */
 	if (chip->options & NAND_SKIP_BBTSCAN)
-		return 0;
+		chip->options |= NAND_BBT_SCANNED;
 
-	/* Build bad block table */
-	return chip->scan_bbt(mtd);
+	return 0;
 }
 EXPORT_SYMBOL(nand_scan_tail);