drm/amdgpu: covert ras status to kernel errno

The original codes use ras status and kernl errno together in the same
function, which is a wrong code style.

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