drm/amd/display: Fix slab-use-after-free on hdcp_work

drm/amd/display: Fix slab-use-after-free on hdcp_work

[Why]
A slab-use-after-free is reported when HDCP is destroyed but the
property_validate_dwork queue is still running.

[How]
Cancel the delayed work when destroying workqueue.

Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/4006
Fixes: da3fd7ac0bcf ("drm/amd/display: Update CP property based on HW query")
Cc: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Tom Chung <chiahsuan.chung@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>