PCI/AER: Initialize aer_fifo

PCI/AER: Initialize aer_fifo

Previously we did not call INIT_KFIFO() for aer_fifo.  This leads to
kfifo_put() sometimes returning 0 (queue full) when in fact it is not.

It is easy to reproduce the problem by using aer-inject:

  $ aer-inject -s :82:00.0 multiple-corr-nonfatal

The content of the multiple-corr-nonfatal file is as below:

  AER
  COR RCVR
  HL 0 1 2 3
  AER
  UNCOR POISON_TLP
  HL 4 5 6 7

Fixes: d7b0ab7c29fc ("PCI/AER: Use kfifo for tracking events instead of reimplementing it")
Link: https://lore.kernel.org/r/1579767991-103898-1-git-send-email-liudongdong3@huawei.com
Signed-off-by: Dongdong Liu <liudongdong3@huawei.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>