drm/amdgpu: Don't ignore rc from drm_dp_mst_topology_mgr_resume()

drm_dp_mst_topology_mgr_resume() returns whether or not it managed to
find the topology in question after a suspend resume cycle, and the
driver is supposed to check this value and disable MST accordingly if
it's gone-in addition to sending a hotplug in order to notify userspace
that something changed during suspend.

Currently, amdgpu just makes the mistake of ignoring the return code
from drm_dp_mst_topology_mgr_resume() which means that if a topology was
removed in suspend, amdgpu never notices and assumes it's still
connected which leads to all sorts of problems.

So, fix this by actually checking the rc from
drm_dp_mst_topology_mgr_resume(). Also, reformat the rest of the
function while we're at it to fix the over-indenting.

Signed-off-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Cc: Jerry Zuo <Jerry.Zuo@amd.com>
Cc: <stable@vger.kernel.org> # v4.15+
Link: https://patchwork.freedesktop.org/patch/msgid/20190108211133.32564-2-lyude@redhat.com