drm/amdkfd: Don't clear PT after process killed

drm/amdkfd: Don't clear PT after process killed

If process is killed. the vm entity is stopped, submit pt update job
will trigger the error message "*ERROR* Trying to push to a killed
entity", job will not execute.

Suggested-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Philip Yang <Philip.Yang@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 10c382ec6c6d1e11975a11962bec21cba6360391)
Cc: stable@vger.kernel.org