virtio: net: remove sparse errors

commit 3fa2a1df (virtio-net: per cpu 64 bit stats (v2)) added extra
__percpu qualifiers and sparse errors.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Stephen Hemminger <shemminger@vyatta.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: David S. Miller <davem@davemloft.net>