BUILD: ssl: fix two remaining occurrences of #if USE_OPENSSL

One was in backend.c and the other one in hlua.c. No other candidate
was found with "git grep '^#if\s*USE'". It's worth noting that 3
other such tests exist for SSL_OP_NO_{SSLv3,TLSv1_1,TLSv1_2} but
that these ones are properly set to 0 in openssl-compat.h when not
defined.

(cherry picked from commit b131049eb5ba5b0e7c02eea10ce9763da4428abe)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>
diff --git a/src/hlua.c b/src/hlua.c
index 80e3ead..4b3d539 100644
--- a/src/hlua.c
+++ b/src/hlua.c
@@ -8593,7 +8593,7 @@
 	char *err = NULL;
 	struct hlua_function *fcn;
 
-#if USE_OPENSSL
+#if defined(USE_OPENSSL)
 	/* Initialize SSL server. */
 	if (socket_ssl->xprt->prepare_srv) {
 		int saved_used_backed = global.ssl_used_backend;