ath10k: fix unregister deadlock when fw probe fails

If firmware probing worker failed it called
device_release_driver() which synchronously called
remove() pci callback. The callback in turn waited
for the worker that called it to finish resulting
in a deadlock.

Waiting for a completion instead of a worker, like
some other drivers do, doesn't seem like the best
idea either:

  Syscall                 Worker

                          probe_fw()
  rmmod
  dev_lock()
  pci->remove()
  wait_for_completion()
                          complete_all()
                          device_release_driver()
                          dev_lock()
                          [sleep]
  free(ar)
  dev_unlock()
                          [resume]

There's no guarantee that Worker upon resuming can
still access any data/code of the module.

Leaving device bound to a driver is not as harmful
as deadlocking so remove the call to
device_release_driver() while a proper solution is
figured out.

Signed-off-by: Michal Kazior <michal.kazior@tieto.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>