nand: raw: mxs_nand: Fix specific hook registration

Move the hook after nand_scan_tail is called. The hook must be replaced
to the mxs specific one but those must to be assignment later in the
probe function.

With this fix markbad is working again. Before this change:

nand markbad 0xDEC00
NXS NAND: Writing OOB isn't supported
NXS NAND: Writing OOB isn't supported
block 0x000dec00 NOT marked as bad! ERROR 0

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