libsecureboot: avoid recusion in ve_trust_init

set our guard value immediately.
also replace call to ve_trust_init in opgp_sig.c:initialize with
call to openpgp_trust_init.

Reported by:	mindal@semihalf.com
Reviewed by:	jhibbits obrien
MFC after:	1 week

lib/libsecureboot/openpgp/opgp_sig.c

@@ -67,9 +67,7 @@ __FBSDID("$FreeBSD$");
 void
 initialize (void)
 {
-#ifdef _STANDALONE
-    ve_trust_init();
-#endif
+	openpgp_trust_init();
 }
 
 #else

lib/libsecureboot/vets.c

@@ -345,7 +345,7 @@ ve_trust_init(void)
 
 	if (once >= 0)
 		return (once);
-
+	once = 0;			/* to be sure */
 	ve_utc_set(time(NULL));
 #ifdef BUILD_UTC
 	ve_utc_set(BUILD_UTC);		/* just in case */