ACPI: scan: Rearrange code related to acpi_get_device_data()

There are two callers of acpi_get_device_data(), acpi_bus_get_device()
and acpi_bus_get_acpi_device(), but only one of them takes the int
return value into account.  Moreover, the latter knows that it passes
a valid return pointer to acpi_get_device_data() and it properly
clears that pointer upfront, so it doesn't need acpi_get_device_data()
to do that.

For this reason, rearrange acpi_get_device_data() to return a strct
acpi_device pointer instead of an int and adapt its callers to that.

While at it, rename acpi_get_device_data() to handle_to_device(),
because the old name does not really reflect the functionality
provided by that function.

No intentional functional impact.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>