drm/amdgpu: fix sysfs interface pcie_replay_count error on navi asic

the asic callback function of get_pcie_replay_count is not implement on navi asic,
it will cause null pinter error when read this interface.

Signed-off-by: Kevin Wang <kevin1.wang@amd.com>
Reviewed-by: Kent Russell <kent.russell@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>