drm/amd/amdgpu: fix the inst passed to amdgpu_virt_rlcg_reg_rw

the inst passed to amdgpu_virt_rlcg_reg_rw should be physical instance.
Fix the miss matched code.

Signed-off-by: Victor Zhao <Victor.Zhao@amd.com>
Reviewed-by: Lijo Lazar <lijo.lazar@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>