drm/amdgpu/gfx6: fix CSIB handling

[ Upstream commit 8307ebc15c1ea98a8a0b7837af1faa6c01514577 ]

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>