ionic: use timer_shutdown_sync

When stopping the watchdog timer at remove time we should
be using the new timer_shutdown_sync to assure the timer
doesn't ever get rearmed.

Signed-off-by: Shannon Nelson <shannon.nelson@amd.com>
Reviewed-by: Brett Creeley <brett.creeley@amd.com>
Signed-off-by: David S. Miller <davem@davemloft.net>