PCI/DOE: Fix destroy_work_on_stack() race

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

PCI/DOE: Fix destroy_work_on_stack() race

The following debug object splat was observed in testing:

ODEBUG: free active (active state 0) object: 0000000097d23782 object type: work_struct hint: doe_statemachine_work+0x0/0x510

WARNING: CPU: 1 PID: 71 at lib/debugobjects.c:514 debug_print_object+0x7d/0xb0

...

Workqueue: pci 0000:36:00.0 DOE [1 doe_statemachine_work

RIP: 0010:debug_print_object+0x7d/0xb0

...

Call Trace:

? debug_print_object+0x7d/0xb0

? __pfx_doe_statemachine_work+0x10/0x10

debug_object_free.part.0+0x11b/0x150

doe_statemachine_work+0x45e/0x510

process_one_work+0x1d4/0x3c0

This occurs because destroy_work_on_stack() was called after signaling

the completion in the calling thread. This creates a race between

destroy_work_on_stack() and the task->work struct going out of scope in

pci_doe().

Signal the work complete after destroying the work struct. This is safe

because signal_task_complete() is the final thing the work item does and

the workqueue code is careful not to access the work struct after.