net:ethernet:aquantia: Missing spinlock initialization.

Fix for missing initialization aq_ring header.lock spinlock.

Fixes: 018423e9 ("net: ethernet: aquantia: Add ring support code")

Signed-off-by: Pavel Belous <pavel.belous@aquantia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>