drm/amdgpu: Fix undue fallthroughs in golden registers initialization

As I was staring at the si_init_golden_registers code, I noticed that
the Pitcairn initialization silently falls through the Cape Verde
initialization, and the Oland initialization falls through the Hainan
initialization. However there is no comment stating that this is
intentional, and the radeon driver doesn't have any such fallthrough,
so I suspect this is not supposed to happen.

Signed-off-by: Jean Delvare <jdelvare@suse.de>
Fixes: 62a37553 ("drm/amdgpu: add si implementation v10")
Cc: Ken Wang <Qingqing.Wang@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: "Marek Olšák" <maraeo@gmail.com>
Cc: "Christian König" <christian.koenig@amd.com>
Cc: Flora Cui <Flora.Cui@amd.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org