ACPI / scan: Set flags.match_driver in acpi_bus_scan_fixed()

Before commit 6931007c (ACPI / scan: Start matching drivers
after trying scan handlers) the match_driver flag for all devices
was set in acpi_add_single_object(), but now it is set by
acpi_bus_device_attach() which is not called for the "fixed"
devices added by acpi_bus_scan_fixed().  This means that
flags.match_driver is never set for those devices now, so make
acpi_bus_scan_fixed() set it before calling device_attach().

Fixes: 6931007c (ACPI / scan: Start matching drivers after trying scan handlers)
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>