drm/amdgpu: Calculate EEPROM table ras info bytes sum

It's more reasonable to check EEPROM table ras info bytes.

Signed-off-by: Stanley.Yang <Stanley.Yang@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>