Fix a memory leak in an error path

Found by Coverity.
Reviewed-by: NRich Salz <rsalz@openssl.org>
Reviewed-by: NPaul Dale <paul.dale@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/5336)

crypto/rsa/rsa_mp.c

@@ -51,6 +51,7 @@ RSA_PRIME_INFO *rsa_multip_info_new(void)
     BN_free(pinfo->d);
     BN_free(pinfo->t);
     BN_free(pinfo->pp);
+    OPENSSL_free(pinfo);
     return NULL;
 }