drm/amd/amdgpu: Cancel the hrtimer in sw_fini

Move the process of cancelling hrtimer to sw_fini

Signed-off-by: Roy Sun <Roy.Sun@amd.com>
Reviewed-by: Emily Deng <Emily.Deng@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>