util/sconfig: Report which key is duplicate

It slightly helps debugging issues when you know what to look out for.

Change-Id: I21eafaf8291701316aa920e458ba74535121b0a1
Signed-off-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/47103
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Martin Roth <martinroth@google.com>
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
diff --git a/util/sconfig/main.c b/util/sconfig/main.c
index a7b2ce6..1fd4404 100644
--- a/util/sconfig/main.c
+++ b/util/sconfig/main.c
@@ -872,7 +872,7 @@
 	for (cur = *head; cur != NULL; prev = cur, cur = cur->next) {
 		const int sort = strcmp(r->key, cur->key);
 		if (sort == 0) {
-			printf("ERROR: duplicate 'register' key.\n");
+			printf("ERROR: duplicate 'register' key '%s'.\n", r->key);
 			exit(1);
 		}
 		if (sort < 0)