drm/amdgpu: correct the gpu reset handling for job != NULL case

Current code wrongly treat all cases as job == NULL.

Signed-off-by: Evan Quan <evan.quan@amd.com>
Reviewed-and-tested-by: Jane Jian <Jane.Jian@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>