usb: typec: tcpm: fix use-after-free case in tcpm_register_source_caps

In the Linux kernel, the following vulnerability has been resolved:

usb: typec: tcpm: fix use-after-free case in tcpm_register_source_caps

There could be a potential use-after-free case in

tcpm_register_source_caps(). This could happen when:

* new (say invalid) source caps are advertised

* the existing source caps are unregistered

* tcpm_register_source_caps() returns with an error as

usb_power_delivery_register_capabilities() fails

This causes port->partner_source_caps to hold on to the now freed source

caps.

Reset port->partner_source_caps value to NULL after unregistering

existing source caps.