tg3: Fix race condition in tg3_get_stats64()

commit 0f566b208b41918053b2e67399673aaec02dde5d upstream.

Spinlock should be taken before checking for tp->hw_stats.

Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>