ACPI / hotplug: Fix acpi_bus_get_device() return value check

Since acpi_bus_get_device() returns a plain int and not acpi_status,
ACPI_FAILURE() should not be used for checking its return value.  Fix
that.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Toshi Kani <toshi.kani@hp.com>