e1000e: fix stats locking in e1000_watchdog_task

Just move the unlock down a bit because it unlocks too
early leaving a chance for get_stats64() run in parallel
while it is still accessing the stats.

Signed-off-by: Flavio Leitner <fleitner@redhat.com>
Acked-by: Bruce Allan <bruce.w.allan@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>