drm/amdgpu: cancel late_init_work before gpu reset

gpu reset will run late_init and schedule the late_init_work.  if we
keep triggering gpu reset in a short time, there are potenial races.

Signed-off-by: xinhui pan <xinhui.pan@amd.com>
Reviewed-by: Feifei Xu <Feifei.Xu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>