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>

notes-merge.c

@@ -113,6 +113,7 @@ static struct notes_merge_pair *find_notes_merge_pair_pos(
 }
 
 static struct object_id uninitialized = {
+	.hash =
 	"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" \
 	"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff"
 };