tests/chamelium/kms_chamelium_hpd: don't unplug multiple times

chamelium_reset_state will unplug all the ports,
prevent unplugging multiple times

Fixes: drm/xe/kernel#3505


Signed-off-by: Kunal Joshi <kunal1.joshi@intel.com>
Reviewed-by: Jeevan B <jeevan.b@intel.com>