drm/amdgpu/vcn: fix typo error

Fix typo error, should be inst_idx instead of inst.

Signed-off-by: James Zhu <James.Zhu@amd.com>
Reviewed-by: Leo Liu <leo.liu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
1 file changed