drm/amdgpu/vcn5.0.1: use correct dpm helper

The VCN and UVD helpers were split in
commit ff69bba0 ("drm/amd/pm: add inst to dpm_set_powergating_by_smu")
However, this happened in parallel to the vcn 5.0.1
development so it was missed there.

Fixes: 346492f3 ("drm/amdgpu: Add VCN_5_0_1 support")
Reviewed-by: Lijo Lazar <lijo.lazar@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: Sonny Jiang <sonjiang@amd.com>
Cc: Boyuan Zhang <boyuan.zhang@amd.com>