checkpolicy: fix gcc -Wsign-compare warnings

Acked-by: Steve Lawrence <slawrence@tresys.com>
diff --git a/checkpolicy/checkpolicy.c b/checkpolicy/checkpolicy.c
index 9881dd7..7fa37af 100644
--- a/checkpolicy/checkpolicy.c
+++ b/checkpolicy/checkpolicy.c
@@ -291,7 +291,7 @@
 
 int display_bools()
 {
-	int i;
+	uint32_t i;
 
 	for (i = 0; i < policydbp->p_bools.nprim; i++) {
 		printf("%s : %d\n", policydbp->p_bool_val_to_name[i],