drm/amdgpu: Clear garbage data in err_data before usage

Memory of err_data should be cleaned before usage
when there're multiple entry in ras ih.
Otherwise garbage data from last loop will be used.

Signed-off-by: Jiawei Gu <Jiawei.Gu@amd.com>
Reviewed-by: Tao Zhou <tao.zhou1@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>