PCI/ACPI: Remove acpi_root_driver in reverse order

Call the sub-driver .remove() methods in the reverse order of the
.add() methods for symmetry.

[bhelgaas: changelog]
Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>