mtd: eLBC NAND: utilize oob_required parameter

Don't read OOB if the caller doesn't require it.

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Reviewed-by: Scott Wood <scottwood@freescale.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>