arm: mach-imx: cmd_nandbcb fix bad block handling

The badblock should be skipped properly in reading and writing.
Fix the logic. The bcb struct is written, skipping the bad block,
so we need to read using the same logic. This was tested create
bad block in the area and then flash it and read it back.

Acked-by: Han Xu <han.xu@nxp.com>
Tested-By: Tim Harvey <tharvey@gateworks.com>
Signed-off-by: Michael Trimarchi <michael@amarulasolutions.com>