ACPI: fix a regression of ACPI device driver autoloading

commit 3620f2f2 sets the cid of
ACPI video/dock/bay device and leaves the hid empty.
As a result, "modalias" should export the cid for
devices which don't have a hid.

ACPI Video driver is not autoloaded with
commit 3620f2f2 applied.
"cat /sys/.../device:03(acpi video bus)/modalias" shows nothing.

ACPI Video driver is autoloaded after revert that commit.
"cat /sys/.../LNXVIDEO:0x/modalias" shows "acpi:LNXVIDEO:"

ACPI Video driver is autoloaded with commit
3620f2f2

 and this patch applied.
"cat /sys/.../device:03(acpi video bus)/modalias"
shows "acpi:LNXVIDEO:"

Signed-off-by: Zhang Rui <rui.zhang@intel.com>
Acked-by: Thomas Renninger <trenn@suse.de>
Signed-off-by: Len Brown <len.brown@intel.com>