drm/amdgpu/vcn: change end doorbell index for vcn_v4_0_3

For sriov, doorbell index for vcn0 for AID needs to be on
32 byte boundary so we need to move the vcn end doorbell

Signed-off-by: Samir Dhume <samir.dhume@amd.com>
Acked-by: Leo Liu <leo.liu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>