Nand: fix PIO support for 8bit devices.

BugLink: http://bugs.launchpad.net/bugs/591249

Signed-off-by: Tawfik Bayouk <tawfik@marvell.com>
Signed-off-by: Eric Miao <eric.miao@canonical.com>
Acked-by: Brad Figg <brad.figg@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>