device_cache_fw_images need to iterate devices in system,
so this patch applies the introduced dpm_for_each_dev to
avoid link failure if CONFIG_FW_LOADER is m.
Reported-by: NFengguang Wu <fengguang.wu@intel.com>
Signed-off-by: NMing Lei <ming.lei@canonical.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>