[MTD] [NAND] drivers/mtd/nand/nandsim.c: remove duplicated #include

Removed duplicated include <asm/div64.h> in
drivers/mtd/nand/nandsim.c.

Signed-off-by: Huang Weiyi <weiyi.huang@gmail.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>