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/transformed.c b/clients/transformed.c
index 75c1250..8983bb5 100644
--- a/clients/transformed.c
+++ b/clients/transformed.c
@@ -264,7 +264,7 @@
 			usage(EXIT_FAILURE);
 	}
 
-	d = display_create(argc, argv);
+	d = display_create(&argc, argv);
 	if (d == NULL) {
 		fprintf(stderr, "failed to create display: %m\n");
 		return -1;