Pass argc pointer to parse_options()

This lets us keep argc up to date as the backend picks out arguments
from the argv array.
diff --git a/clients/calibrator.c b/clients/calibrator.c
index 3b9f2fc..cc6f4ed 100644
--- a/clients/calibrator.c
+++ b/clients/calibrator.c
@@ -238,7 +238,7 @@
 	struct display *display;
 	struct calibrator *calibrator;
 
-	display = display_create(argc, argv);
+	display = display_create(&argc, argv);
 
 	if (display == NULL) {
 		fprintf(stderr, "failed to create display: %m\n");