mtd: introduce mtd_can_have_bb helper

This patch introduces new 'mtd_can_have_bb()' helper function which checks
whether the flash can have bad eraseblocks. Then it changes all the
direct 'mtd->block_isbad' use cases with 'mtd_can_have_bb()'.

Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

drivers/mtd/ubi/build.c

@@ -664,7 +664,7 @@ static int io_init(struct ubi_device *ubi)
 	ubi->peb_count  = mtd_div_by_eb(ubi->mtd->size, ubi->mtd);
 	ubi->flash_size = ubi->mtd->size;
 
-	if (ubi->mtd->block_isbad && ubi->mtd->block_markbad)
+	if (mtd_can_have_bb(ubi->mtd))
 		ubi->bad_allowed = 1;
 
 	if (ubi->mtd->type == MTD_NORFLASH) {