usb: typec: ucsi: Fix race condition and ordering in port unregistration

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

usb: typec: ucsi: Fix race condition and ordering in port unregistration

A synchronization issue exists during port unregistration where pending
partner work items can race against workqueue destruction, leading to
use-after-free conditions:

cros_ec_ucsi cros_ec_ucsi.3.auto: error -ETIMEDOUT: PPM init failed
BUG: kernel NULL pointer dereference, address: 0000000000000000
RIP: 0010:__queue_work+0x83/0x4a0
Call Trace:
<IRQ>
__cfi_delayed_work_timer_fn+0x10/0x10
run_timer_softirq+0x3b6/0xbd0
sched_clock_cpu+0xc/0x110
irq_exit_rcu+0x18d/0x330
fred_sysvec_apic_timer_interrupt+0x5e/0x80

Fix this by ensuring strict ordering and proper serialization during
teardown:

1. Move ucsi_unregister_partner() to the beginning of the teardown
sequence and protect it under the connector mutex lock.
2. Ensure all pending partner tasks are explicitly flushed and finished
before the workqueue is destroyed.
3. Switch from mod_delayed_work() to a cancel_delayed_work() and
queue_delayed_work() sequence. This guarantees that items currently marked
as pending won't be scheduled an additional time, preventing a double
release of resources which leads to the following crash:

Oops: general protection fault, probably for non-canonical address
0xdead000000000122: 0000 [#1] SMP NOPTI
Workqueue: cros_ec_ucsi.3.auto-con2 ucsi_poll_worker
RIP: 0010:ucsi_poll_worker+0x65/0x1e0
Call Trace:
<TASK>
process_scheduled_works+0x218/0x6d0
worker_thread+0x188/0x3f0
__cfi_worker_thread+0x10/0x10
kthread+0x226/0x2a0

To ensure these rules are applied identically across both the normal
teardown and the ucsi_init() error paths, consolidate the cleanup logic
into a new helper, ucsi_unregister_port().