fip_create: Fix exit status for missing output filename

Change-Id: I0d298eea9eaf47121c87637c7395e5d9868aa272
diff --git a/tools/fip_create/fip_create.c b/tools/fip_create/fip_create.c
index 7bce348..48cb3f6 100644
--- a/tools/fip_create/fip_create.c
+++ b/tools/fip_create/fip_create.c
@@ -811,7 +811,7 @@
 	if (fip_filename == NULL) {
 		printf("ERROR: Missing FIP filename\n");
 		print_usage();
-		return 0;
+		return EINVAL;
 	}
 
 	/* Unpack images from FIP always takes precedence over packaging. In