Fix register usage of SPCI_SUCCESS.

Change-Id: Iab5b5d2a5f98a069d90a09d721c1d66a9f142994
diff --git a/src/api.c b/src/api.c
index 5261688..92328c8 100644
--- a/src/api.c
+++ b/src/api.c
@@ -1677,7 +1677,7 @@
 
 	struct spci_value ret = {
 		.func = SPCI_SUCCESS_32,
-		.arg1 = (SPCI_VERSION_MAJOR << SPCI_VERSION_MAJOR_OFFSET) |
+		.arg2 = (SPCI_VERSION_MAJOR << SPCI_VERSION_MAJOR_OFFSET) |
 			SPCI_VERSION_MINOR};
 	return ret;
 }