hw: Remove unused 'hw/devices.h' include

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: BALATON Zoltan <balaton@eik.bme.hu>
Tested-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>