drm/i915: Don't send MST hotplugs during resume

We have a bad habit of calling drm_fb_helper_hotplug_event() far more
then we actually need to. MST appears to be one of these cases, where we
call drm_fb_helper_hotplug_event() if we fail to resume a connected MST
topology in intel_dp_mst_resume(). We don't actually need to do this at
all though since hotplug events are already sent from
drm_dp_connector_destroy_work() every time connectors are unregistered
from userspace's PoV. Additionally, extra calls to
drm_fb_helper_hotplug_event() also just mean more of a chance of doing a
connector probe somewhere we shouldn't.

So, don't send any hotplug events during resume if the MST topology
fails to come up. Just rely on the DP MST helpers to send them for us.

Signed-off-by: Lyude Paul <lyude@redhat.com>
Cc: Imre Deak <imre.deak@intel.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190129191001.442-3-lyude@redhat.com