drm/amdgpu: correct clock info for SRIOV

Currently, get clock info from default clk of pm if dpm is disable.
Buf SRIOV doesn't support dpm and pm, can't get anything from pm.
Only get clock info only from default clk of amdgpu for SRIOV.

And driver get pm default clk also from amdgpu default clk and never
be changed by others. So use amdgpu default clk value for SRIOV
and non-dpm cases.

Signed-off-by: Xiangliang Yu <Xiangliang.Yu@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>