mtd: return badblockbits back

In commit c7b28e25cb9beb943aead770ff14551b55fa8c79 the initialization of
the backblockbits was accidentally removed. This patch returns it back,
because otherwise some NAND drivers are broken.

This problem was reported by "Saxena, Parth <parth.saxena@ti.com>" here:
http://lists.infradead.org/pipermail/linux-mtd/2011-April/035221.html

Reported-by: Saxena, Parth <parth.saxena@ti.com>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Tested-by: Saxena, Parth <parth.saxena@ti.com>
Acked-by: Saxena, Parth <parth.saxena@ti.com>
Acked-by: Brian Norris <computersforpeace@gmail.com>
Cc: stable@kernel.org [2.6.36+]
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>