hisi_lpc: Use acpi_dev_for_each_child()

hisi_lpc: Use acpi_dev_for_each_child()

Instead of walking the list of children of an ACPI device directly,
use acpi_dev_for_each_child() to carry out an action for all of
the given ACPI device's children.

This will help to eliminate the children list head from struct
acpi_device as it is redundant and it is used in questionable ways
in some places (in particular, locking is needed for walking the
list pointed to it safely, but it is often missing).

While at it, simplify hisi_lpc_acpi_set_io_res() by making it accept
a struct acpi_device pointer from the caller, instead of going to
struct device and back to get the same result, and clean up confusion
regarding hostdev and its ACPI companion in that function.

Also remove a redundant check from it.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: John Garry <john.garry@huawei.com>