drm/amd/display: Clear connector's edid pointer

Clear connector's edid pointer on coonnector update, when unplugging
the display.

Fix poison EDID when hotplugging on previously used connector.

Signed-off-by: Mikita Lipski <mikita.lipski@amd.com>
Reviewed-by: Harry Wentland <Harry.Wentland@amd.com>
Cc: stable@vger.kernel.org
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>