virtio_console: Constify some static variables

virtio_console: Constify some static variables

The id_table and feature_table pointers in struct virtio_driver are
pointers to const. Mark the corresponding static variables const to
allow the compiler to put them in read-only memory.

Before:
   text    data     bss     dec     hex filename
  25447     713      76   26236    667c drivers/char/virtio_console.o

After:
   text    data     bss     dec     hex filename
  25488     673      76   26237    667d drivers/char/virtio_console.o

Signed-off-by: Rikard Falkeborn <rikard.falkeborn@gmail.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Amit Shah <amit@kernel.org>
Link: https://lore.kernel.org/r/20200701200950.30314-6-rikard.falkeborn@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>