usb: typec: ucsi: Fix NULL pointer dereference

Making sure the UCSI debugfs entry actually exists before
attempting to remove it.

Fixes: df0383f ("usb: typec: ucsi: Add debugfs for ucsi commands")
Reported-by: Dave Hansen <dave.hansen@intel.com>
Closes: https://lore.kernel.org/linux-usb/700df3c4-2f6c-85f9-6c61-065bc5b2db3a@intel.com/
Suggested-by: Dave Hansen <dave.hansen@intel.com>
Suggested-by: Mario Limonciello <mario.limonciello@amd.com>
Cc: Saranya Gopal <saranya.gopal@intel.com>
Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Cc: Thorsten Leemhuis <regressions@leemhuis.info>
Link: https://lore.kernel.org/r/20230906084842.1922052-1-heikki.krogerus@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: Heikki Krogerus

drivers/usb/typec/ucsi/debugfs.c

@@ -84,6 +84,9 @@ void ucsi_debugfs_register(struct ucsi *ucsi)
 
 void ucsi_debugfs_unregister(struct ucsi *ucsi)
 {
+	if (IS_ERR_OR_NULL(ucsi) || !ucsi->debugfs)
+		return;
+
 	debugfs_remove_recursive(ucsi->debugfs->dentry);
 	kfree(ucsi->debugfs);
 }