ptp: idt82p33: Stop PTP work producers before teardown

idt82p33_ptp_clock_unregister_all() cancels each channel's adjtime work
before unregistering its PTP clock. An adjustment callback already in
progress can schedule that work after cancellation returns. Device
removal then frees the channel while its delayed work remains queued,
causing a use-after-free.

Mark the device as stopping under its lock before draining work. Reject
new adjustment and EXTS requests, clear the EXTS polling mask, and
synchronously drain the EXTS and channel adjustment work before the
device storage is released.

With an i2c-stub device and kprobe-controlled callback timing, three
runs of the unmodified driver reported KASAN use-after-free after
unbind. Three runs with this change completed without a kernel
diagnostic. No physical IDT82P33 device was tested.

Cc: stable+noautosel@kernel.org # untested fix to a driver init path race
Signed-off-by: Yibo Tan <lhfff@tju.edu.cn>
Link: https://patch.msgid.link/20260922113601.855416-1-lhfff@tju.edu.cn
Signed-off-by: Jakub Kicinski <kuba@kernel.org>