mtd: nand: assign mtd->name in find_full_id_nand

This patch assigned the type->name to mtd->name when mtd->name is
NULL in function "find_full_id_nand".
mtd->name is NULL may cause some problem.

Signed-off-by: Cai Zhiyong <caizhiyong@huawei.com>
Acked-by: Huang Shijie <b32955@freescale.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>