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>

engines/e_chil.c

@@ -786,7 +786,7 @@ static EVP_PKEY *hwcrhk_load_privkey(ENGINE *eng, const char *key_id,
         goto err;
     }
 #  ifndef OPENSSL_NO_RSA
-    hptr = OPENSSL_malloc(sizeof(HWCryptoHook_RSAKeyHandle));
+    hptr = OPENSSL_malloc(sizeof(*hptr));
     if (!hptr) {
         HWCRHKerr(HWCRHK_F_HWCRHK_LOAD_PRIVKEY, ERR_R_MALLOC_FAILURE);
         goto err;