drm/amdgpu/gfx8: fix CSIB handling

[ Upstream commit c8b8d7a4f1c5cdfbd61d75302fb3e3cdefb1a7ab ]

We shouldn't return after the last section.
We need to update the rest of the CSIB.

Reviewed-by: Rodrigo Siqueira <siqueira@igalia.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>