netfilter: nf_tables: remove assignment with no effect in chain blob builder

cppcheck possible warnings:

>> net/netfilter/nf_tables_api.c:2014:2: warning: Assignment of function parameter has no effect outside the function. Did you forget dereferencing it? [uselessAssignmentPtrArg]
    ptr += offsetof(struct nft_rule_dp, data);
    ^
Reported-by: Nkernel test robot <yujie.liu@intel.com>
Signed-off-by: NPablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nf_tables_api.c

@@ -2011,7 +2011,6 @@ static void nft_last_rule(struct nft_rule_blob *blob, const void *ptr)
 
 	prule = (struct nft_rule_dp *)ptr;
 	prule->is_last = 1;
-	ptr += offsetof(struct nft_rule_dp, data);
 	/* blob size does not include the trailer rule */
 }