virtio: console: comment cleanup

Remove old lguest-style comments.

[Amit: - wingify comments acc. to kernel style
       - indent comments ]

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>