We need to schedule the smu AC/DC interrupt ack to avoid
potentially sleeping if the smu message mutex is contended.

Fixes: e1188aac ("drm/amdgpu/smu11: add support for SMU AC/DC interrupts")
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>