drm/amdgpu: fix the memory override in kiq ring struct

This is introduced by the code merge and will let the
adev->gfx.kiq[0].ring struct being overrided

Signed-off-by: Shiwu Zhang <shiwu.zhang@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>