drm/amdgpu: Fix NULL pointer when load kfd driver with PP block is disabled

When PP block is disabled, return a fix value(100M) for mclk and sclk on
bare-metal mode. This will cover the emulation mode as well.

Signed-off-by: Shaoyun Liu <Shaoyun.Liu@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>