UPSTREAM: PCI/pwrctrl: Cancel outstanding rescan work when unregistering

It's possible to trigger use-after-free here by:

  (a) forcing rescan_work_func() to take a long time and
  (b) utilizing a pwrctrl driver that may be unloaded for some reason

Cancel outstanding work to ensure it is finished before we allow our data
structures to be cleaned up.

[bhelgaas: tidy commit log]
Bug: 415347036
Fixes: 8f62819a ("PCI/pwrctl: Rescan bus on a separate thread")
Change-Id: Ia319526ed4ef06bec3180378c9a008340cec9658
Signed-off-by: Brian Norris <briannorris@google.com>
Signed-off-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Acked-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Cc: Konrad Dybcio <konradybcio@kernel.org>
Link: https://patch.msgid.link/20250409115313.1.Ia319526ed4ef06bec3180378c9a008340cec9658@changeid
(cherry picked from commit 8b926f23)