cleanup 1 << 31 idioms

Index: lib/krb5/krb5.h
--- lib/krb5/krb5.h.orig
+++ lib/krb5/krb5.h
@@ -426,7 +426,7 @@ typedef union {
 #define KDC_OPT_RENEWABLE_OK		(1 << 27)
 #define KDC_OPT_ENC_TKT_IN_SKEY		(1 << 28)
 #define KDC_OPT_RENEW			(1 << 30)
-#define KDC_OPT_VALIDATE		(1 << 31)
+#define KDC_OPT_VALIDATE		(1U << 31)
 
 typedef union {
     KDCOptions b;