misc *.c: use designated initializers for struct assignments

Change a few miscellaneous non-designated initializer assignments to
use designated initializers.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/object-file.c b/object-file.c
index bdc5cbd..f0a75b3 100644
--- a/object-file.c
+++ b/object-file.c
@@ -274,10 +274,11 @@ static struct cached_object {
 static int cached_object_nr, cached_object_alloc;
 
 static struct cached_object empty_tree = {
-	{ EMPTY_TREE_SHA1_BIN_LITERAL },
-	OBJ_TREE,
-	"",
-	0
+	.oid = {
+		.hash = EMPTY_TREE_SHA1_BIN_LITERAL,
+	},
+	.type = OBJ_TREE,
+	.buf = "",
 };
 
 static struct cached_object *find_cached_object(const struct object_id *oid)