virtio-input: const_le16 and const_le32 not build time constant

As the implementation of const_le16 and const_le32 is not build time constant
on big endian systems this need to be fixed.

  CC    hw/input/virtio-input-hid.o
hw/input/virtio-input-hid.c:340:13: error: initializer element is not constant
hw/input/virtio-input-hid.c:340:13: error: (near initialization for ‘virtio_keyboard_config[1].u.ids.bustype’)
...

Signed-off-by: Michael Mueller <mimu@linux.vnet.ibm.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
