mtd: report all bad block as 1

mtd: report all bad block as 1

PD#145359: mtd: report factory bad block as used bad one to mtd.

nandwrite in mtd utilies identify bad blocks by checking whether
return value of mtd_block_isbad is 1;
Our host driver need to distinguish used(1)/factory(FACTORY_BAD_BLOCK_ERROR)
bad block because partition table caculation cares factory bad ones only.

As mtd->_block_isbad is called by inside usage, so we normalize all the bad
block return value in mtd_block_isbad.

Change-Id: I19b0f25ce93ce527b6e02d59330b2edaf61020d4
Signed-off-by: Yonghui Yu <yonghui.yu@amlogic.com>