Use safer sizeof variant in malloc

For a local variable:
        TYPE *p;
Allocations like this are "risky":
        p = OPENSSL_malloc(sizeof(TYPE));
if the type of p changes, and the malloc call isn't updated, you
could get memory corruption.  Instead do this:
        p = OPENSSL_malloc(sizeof(*p));
Also fixed a few memset() calls that I noticed while doing this.

Reviewed-by: Richard Levitte <levitte@openssl.org>

ssl/ssl_cert.c

diff --git a/ssl/ssl_cert.c b/ssl/ssl_cert.c
index cce7f15..c7a2aa9 100644
--- a/ssl/ssl_cert.c
+++ b/ssl/ssl_cert.c
@@ -182,9 +182,8 @@
 
 CERT *ssl_cert_new(void)
 {
-    CERT *ret;
+    CERT *ret = OPENSSL_malloc(sizeof(*ret));
 
-    ret = OPENSSL_malloc(sizeof(CERT));
     if (ret == NULL) {
         SSLerr(SSL_F_SSL_CERT_NEW, ERR_R_MALLOC_FAILURE);
         return (NULL);
@@ -202,10 +201,9 @@
 
 CERT *ssl_cert_dup(CERT *cert)
 {
-    CERT *ret;
+    CERT *ret = OPENSSL_malloc(sizeof(*ret));
     int i;
 
-    ret = OPENSSL_malloc(sizeof(CERT));
     if (ret == NULL) {
         SSLerr(SSL_F_SSL_CERT_DUP, ERR_R_MALLOC_FAILURE);
         return (NULL);
@@ -577,13 +575,13 @@
 {
     SESS_CERT *ret;
 
-    ret = OPENSSL_malloc(sizeof *ret);
+    ret = OPENSSL_malloc(sizeof(*ret));
     if (ret == NULL) {
         SSLerr(SSL_F_SSL_SESS_CERT_NEW, ERR_R_MALLOC_FAILURE);
         return NULL;
     }
 
-    memset(ret, 0, sizeof *ret);
+    memset(ret, 0, sizeof(*ret));
     ret->peer_key = &(ret->peer_pkeys[SSL_PKEY_RSA_ENC]);
     ret->references = 1;