Revert "mtd: nand: add check for out of page read"

This reverts commit e14feafbe0d5c6d64bb6fe4eba928cb57ac9a4c8.

The commit limits the maximum amount of bytes which can be read
at one go to the OOB size, which is incorrect, because mtd->read_oob()
allows reading multiple pages at a time, see comment near
"struct mtd_oob_ops" at include/linux/mtd/mtd.h. So this patch
breaks ABI and hence, has to be reverted.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>