Fix no-ec --strict-warnings builds

The 'loop' variable is only used if EC is available.
Reviewed-by: NRich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/5149)

apps/speed.c

@@ -1277,7 +1277,9 @@ int speed_main(int argc, char **argv)
     || !defined(OPENSSL_NO_EC)
     long rsa_count = 1;
 #endif
+#ifndef OPENSSL_NO_EC
     size_t loop;
+#endif
 
     /* What follows are the buffers and key material. */
 #ifndef OPENSSL_NO_RC5