netfilter: xt_quota: Don't use aligned attribute in sizeof

Clang warns:

net/netfilter/xt_quota.c:47:44: warning: 'aligned' attribute ignored
when parsing type [-Wignored-attributes]
        BUILD_BUG_ON(sizeof(atomic64_t) != sizeof(__aligned_u64));
                                                  ^~~~~~~~~~~~~

Use 'sizeof(__u64)' instead, as the alignment doesn't affect the size
of the type.

Fixes: e9837e55 ("netfilter: xt_quota: fix the behavior of xt_quota module")
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>