netfilter: xt_rateest: fix comparison with self

As noticed by Trk Edwin <edwintorok@gmail.com>:

Compiling the kernel with clang has shown this warning:

net/netfilter/xt_rateest.c:69:16: warning: self-comparison always results in a
constant value
                        ret &= pps2 == pps2;
                                    ^
Looking at the code:
if (info->flags & XT_RATEEST_MATCH_BPS)
            ret &= bps1 == bps2;
        if (info->flags & XT_RATEEST_MATCH_PPS)
            ret &= pps2 == pps2;

Judging from the MATCH_BPS case it seems to be a typo, with the intention of
comparing pps1 with pps2.

http://bugzilla.kernel.org/show_bug.cgi?id=13535

Signed-off-by: Patrick McHardy <kaber@trash.net>