[MTD] [NAND] fix OOPS accessing flash operations over STM flash on PXA

STM 2Gb flash is a large-page NAND flash.  Set operations accordingly.
This field is dereferenced without a check in several places resulting in
OOPS.

Signed-off-by: Denis V. Lunev <den@openvz.org>
Acked-by: Eric Miao <ymiao3@marvell.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>