drm/amdgpu/pm: fix UVD handing in amdgpu_dpm_set_powergating_by_smu()

UVD and VCN were split into separate dpm helpers in commit
ff69bba0 ("drm/amd/pm: add inst to dpm_set_powergating_by_smu")
as such, there is no need to include UVD in the is_vcn variable since
UVD and VCN are handled by separate dpm helpers now. Fix the check.

Fixes: ff69bba0 ("drm/amd/pm: add inst to dpm_set_powergating_by_smu")
Closes: drm/amd#3959
Link: https://lists.freedesktop.org/archives/amd-gfx/2025-February/119827.html


Reviewed-by: Lijo Lazar <lijo.lazar@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: Boyuan Zhang <boyuan.zhang@amd.com>