mtd: sm_rtl: check kmalloc return value

Because malloc/kzalloc may fail, we should check kmalloc/kzalloc return value
 in sm_create_sysfs_attributes(), mtd/sm_rtl.c and do error handling.
Meanwhile, we should check sm_create_sysfs_attributes return value.

Signed-off-by: Xiaochen Wang <wangxiaochen0@gmail.com>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>