[PATCH AUTOSEL 5.10 13/22] drm/amdgpu: install stub fence into potential unused fence pointers

[Bryan Jennings]

This is also causing log spam on 5.15.  It was included in 5.15.128 as 
commit 4921792e04f2125b5eadef9dbe9417a8354c7eff.  I encountered this and 
found https://gitlab.freedesktop.org/drm/amd/-/issues/2820 while 
researching the problem.