ionic: fix vf op lock usage

These are a couple of read locks that should be write locks.

Fixes: fbb39807

 ("ionic: support sr-iov operations")
Signed-off-by: Shannon Nelson <snelson@pensando.io>
Reviewed-by: Parav Pandit <parav@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>