!339 ima: Fix a potential NULL pointer access in ima_restore_measurement_list

Merge Pull Request from: @HuaxinLuGitee 
 
In restore_template_fmt, when kstrdup fails, a non-NULL value will still be
returned, which causes a NULL pointer access in template_desc_init_fields. 
 
Link:https://gitee.com/openeuler/kernel/pulls/339

 
Reviewed-by: Zheng Zengkai <zhengzengkai@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>