drm/amdgpu: record error code when ring test failed

drm/amdgpu: record error code when ring test failed

BugLink: http://bugs.launchpad.net/bugs/1621113
commit 1f703e6679f373f5bba4efe7093aa82e91af4037 upstream.

Otherwise we may miss errors.

Signed-off-by: Chunming Zhou <David1.Zhou@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>