I can't see the debug file attached. If there's a problem attaching it, then please zip it.
But if you say you see the correct voltage, then there's probably no need for the debug file. A screenshot showing both values might be better.
GPU VDDC is the voltage requested by the GPU. GPU VRM Voltage is the voltage passed to the GPU by the voltage regulator. So it's similar to CPU VID and CPU Vcore - VID/VDDC is requested, Vcore/VRM Voltage is the actual voltage (measured on voltage rail).
Thanks for the data. Unfortunately this debug file captures only situation in GPU idle mode - VDDC = 0.850 V. Could you please create a debug file with load on GPU and raised VDDC ?
Anyway - I believe this is a problem of AMD GPU driver which reports such voltage. Have you tried to upgrade the Catalyst drivers ?