drm/amdgpu: fix convert bad page retiremt

Pmfw read ecc info registers and store values in
eccinfo_table in the following order

umc0 ch_inst 0, 1, 2 ... 7
umc1 ch_inst 0, 1, 2 ... 7
...
umc3 ch_inst 0, 1, 2 ... 7

Driver should convert eccinfo_table_idx to channel_index according
to channel_idx_tbl.

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