drm/amdgpu/powerplay/vega10: fix typo in register base index

Probably a copy pasta.  No functional difference, both have
the same value.

Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Reported-by: Michael von Khurja <mvonkhurja@techpowerup.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>