crypto: af_alg - use struct_size() in sock_kfree_s()

Make use of the struct_size() helper instead of an open-coded version
in order to avoid any potential type mistakes, in particular in the
context in which this code is being used.

So, change the following form:

sizeof(*sgl) + sizeof(sgl->sg[0]) * (MAX_SGL_ENTS + 1)

to :

struct_size(sgl, sg, MAX_SGL_ENTS + 1)

This code was detected with the help of Coccinelle.
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto/af_alg.c

@@ -635,8 +635,7 @@ void af_alg_pull_tsgl(struct sock *sk, size_t used, struct scatterlist *dst,
 		}
 
 		list_del(&sgl->list);
-		sock_kfree_s(sk, sgl, sizeof(*sgl) + sizeof(sgl->sg[0]) *
-						     (MAX_SGL_ENTS + 1));
+		sock_kfree_s(sk, sgl, struct_size(sgl, sg, MAX_SGL_ENTS + 1));
 	}
 
 	if (!ctx->used)