drm/amdgpu/vcn: Fix the register setting for vcn1

commit 02fc996d upstream.

Correct the code error for setting register UVD_GFX10_ADDR_CONFIG.
Need to use inst_idx, or it only will set VCN0.

Signed-off-by: Emily Deng <Emily.Deng@amd.com>
Reviewed-by: James Zhu <James.Zhu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>