usb: typec: ucsi: Fix null pointer dereference in trace

In the Linux kernel, the following vulnerability has been resolved: usb: typec: ucsi: Fix null pointer dereference in trace ucsi_register_altmode checks IS_ERR for the alt pointer and treats NULL as valid. When CONFIG_TYPEC_DP_ALTMODE is not enabled, ucsi_register_displayport returns NULL which causes a NULL pointer dereference in trace. Rather than return NULL, call typec_port_register_altmode to register DisplayPort alternate mode as a non-controllable mode when CONFIG_TYPEC_DP_ALTMODE is not enabled.