staging: vchiq_arm: use list_for_each_entry when accessing bulk_waiter_list

The resulting code is way more readeable and intuitive compared to plain
list_for_each.

Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Acked-by: Stefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>