libxtables: fix compile error due to incomplete change

Commit 2338efd8f799d8373dc196c797bda9690283b698 forgot to update
the constant in one place, and the compile error triggered only
when -DNO_SHARED_LIBS (configure --disable-shared) was in effect.

Signed-off-by: Jan Engelhardt <jengelh@medozas.de>
diff --git a/xtables.c b/xtables.c
index 1214127..044603f 100644
--- a/xtables.c
+++ b/xtables.c
@@ -638,7 +638,7 @@
 		else
 			ptr = NULL;
 	}
-	if(!ptr && (tryload == LOAD_MUST_SUCCEED)) {
+	if (ptr == NULL && tryload == XTF_LOAD_MUST_SUCCEED) {
 		xt_params->exit_err(PARAMETER_PROBLEM,
 			   "Couldn't find target `%s'\n", name);
 	}