[MTD] [NAND] Wrong calculation of page number in nand_block_bad()

In case that there is no memory based bad block table available the
function nand_block_checkbad() in drivers/mtd/nand/nand_base.c will call
nand_block_bad() directly. When parameter 'getchip' is set to zero,
nand_block_bad() will not right shift the offset to calculate the
correct page number.

Signed-off-by: Thomas Knobloch <knobloch@siemens.com>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>