NAND: Fix integer overflow in ONFI detection of chips >= 4GiB

This patch sync with David's patch on Linux in nand_flash_detect_onfi()

	commit 4ccb3b4497ce01fab4933704fe21581e30fda1a5
	Author: David Woodhouse <David.Woodhouse@intel.com>
	Date:   Fri Dec 3 16:36:34 2010 +0000

    	mtd: nand: Fix integer overflow in ONFI detection of chips >= 4GiB

Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

Signed-off-by: Florian Fainelli <florian@openwrt.org>