drm/nouveau: Remove useless poll_disable() call in switcheroo_set_state()
This won't do anything but potentially make us miss hotplugs. We already
call drm_kms_helper_poll_disable() in
nouveau_pmops_suspend()->nouveau_display_suspend()->nouveau_display_fini()
Signed-off-by: Lyude Paul <lyude@redhat.com> Reviewed-by: Karol Herbst <kherbst@redhat.com> Acked-by: Daniel Vetter <daniel@ffwll.ch> Cc: Lukas Wunner <lukas@wunner.de> Signed-off-by: Ben Skeggs <bskeggs@redhat.com>