drm/amd/amdgpu: Fix offset for SQ_DEBUG_STS_GLOBAL on gfx10 (v2)

Despite having different IP offsets the computed address of the register(s)
are the same between gfx7..gfx10.  This patch fixes the offset relative
to the GC block on gfx10.

(v2): SQ_DEBUG_STS_GLOBAL2 is 0x10 higher ...

Signed-off-by: Tom St Denis <tom.stdenis@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>