drm/amdgpu: remove the redundant null check

[zhong jiang]

On 2019/9/5 16:38, Markus Elfring wrote:
>>> Were any source code analysis tools involved for finding
>>> these update candidates?
>> With the help of Coccinelle. You can find out some example in scripts/coccinelle/.
> Thanks for such background information.
> Was the script “ifnullfree.cocci” applied here?
Yep
> Will it be helpful to add attribution for such tools
> to any more descriptions in your patches?
Sometimes, I will add the description in my patches. Not always.

Thanks,
zhong jiang
> Regards,
> Markus
>
> .
>