!4012 drm/amdgpu: Fix a null pointer access when the smc_rreg pointer is NULL

Merge Pull Request from: @ci-robot 
 
PR sync from: Baogen Shang <baogen.shang@outlook.com>
https://mailweb.openeuler.org/hyperkitty/list/kernel@openeuler.org/message/KNLAD6EDXJPWCFUEATI3SWNGGTNVF6ZH/ 
 
https://gitee.com/openeuler/kernel/issues/I8AS5P 
 
Link:https://gitee.com/openeuler/kernel/pulls/4012

 

Reviewed-by: sanglipeng <sanglipeng1@jd.com>
Signed-off-by: Jialin Zhang <zhangjialin11@huawei.com>