[MTD] [NAND] Casting bug in nand_default_block_markbad

There is a slight bug in nand_default_block_markbad, where the offset is
cast to an integer, prior to being shifted. This means that on large
offsets, it is incorrectly doing a signed shift & losing bits. Fixed
this by doing the cast after the shift (as is done elsewhere in the code).

Signed-off-by: Andre Renaud <andre@bluewatersys.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>