db: Fix an issue with the memset

We want to memset the entire area of the atuple and not just the
first four/eight bytes of the data.

Fixes: Coverity CID 1040708
diff --git a/openbsc/src/libmsc/db.c b/openbsc/src/libmsc/db.c
index 4e20e23..b57a050 100644
--- a/openbsc/src/libmsc/db.c
+++ b/openbsc/src/libmsc/db.c
@@ -511,7 +511,7 @@
 		return -ENOENT;
 	}
 
-	memset(atuple, 0, sizeof(atuple));
+	memset(atuple, 0, sizeof(*atuple));
 
 	atuple->use_count = dbi_result_get_ulonglong(result, "use_count");
 	atuple->key_seq = dbi_result_get_ulonglong(result, "key_seq");