scsi: qla2xxx: stop timer in shutdown path

In shutdown/reboot paths, the timer is not stopped:

  qla2x00_shutdown
  pci_device_shutdown
  device_shutdown
  kernel_restart_prepare
  kernel_restart
  sys_reboot

This causes lockups (on powerpc) when firmware config space access calls
are interrupted by smp_send_stop later in reboot.

Fixes: e30d1756

 ("[SCSI] qla2xxx: Addition of shutdown callback handler.")
Link: https://lore.kernel.org/r/20191024063804.14538-1-npiggin@gmail.com
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Acked-by: Himanshu Madhani <hmadhani@marvell.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>