mtd: diskonchip: mem resource name is not optional

Passing a name to request_mem_region() isn't optional and can't just
be NULL. Passing NULL causes a NULL ptr deref later in the boot
process.

Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
Tested-by: Alexander Shiyan <shc_work@mail.ru>
Cc: <stable@vger.kernel.org> # 3.14
Signed-off-by: Brian Norris <computersforpeace@gmail.com>