usb: typec: ucsi: displayport: Fix NULL pointer access

This patch ensures that the UCSI driver waits for all pending tasks in the
ucsi_displayport_work workqueue to finish executing before proceeding with
the partner removal.

Cc: stable <stable@kernel.org>
Fixes: af8622f ("usb: typec: ucsi: Support for DisplayPort alt mode")
Signed-off-by: Andrei Kuchynski <akuchynski@chromium.org>
Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Reviewed-by: Benson Leung <bleung@chromium.org>
Link: https://lore.kernel.org/r/20250424084429.3220757-3-akuchynski@chromium.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: Andrei Kuchynski

drivers/usb/typec/ucsi/displayport.c

@@ -299,6 +299,8 @@ void ucsi_displayport_remove_partner(struct typec_altmode *alt)
 	if (!dp)
 		return;
 
+	cancel_work_sync(&dp->work);
+
 	dp->data.conf = 0;
 	dp->data.status = 0;
 	dp->initialized = false;