pds_core: keep the health thread stopped during reset

pds_core: keep the health thread stopped during reset

Commit d9407ff11809 ("pds_core: Prevent health thread from running
during reset/remove") stops the health thread with cancel_work_sync()
before a reset, but a devcmd timeout during pdsc_fw_down() re-queues
health_work, so pdsc_health_thread() runs again mid-reset and double
allocates the core DMA queues via pdsc_fw_up().

Only the reset path is affected: on remove PDSC_S_STOPPING_DRIVER gates
the health thread and the workqueue is destroyed.

Use disable_work_sync() to cancel health_work and block further
queue_work() on it, and enable_work() in pdsc_restart_health_thread() to
re-allow it after the reset.

disable_work_sync() keeps a disable depth, so every disable must be
matched by one enable. pdsc_reset_prepare() stops the health thread and
pdsc_reset_done() restarts it. On the AER path pdsc_pci_error_detected()
calls pdsc_reset_prepare(), then pdsc_pci_error_resume() re-inits via
pci_reset_function_locked() (pds_core has no .slot_reset handler), which
runs the pair again - stopping the thread twice but restarting it once.
Gate the disable and enable on a health_stopped flag so each fires at
most once per stopped/running transition.

Fixes: d9407ff11809 ("pds_core: Prevent health thread from running during reset/remove")
Reported-by: sashiko-bot <sashiko-bot@kernel.org>
Closes: https://sashiko.dev/#/patchset/20260629200358.2626129-1-nikhil.rao%40amd.com?part=2
Signed-off-by: Nikhil P. Rao <nikhil.rao@amd.com>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Link: https://patch.msgid.link/20260727164548.359562-1-nikhil.rao@amd.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>