kernel: hvc_console: Fix race between hvc_close and hvc_remove

[Eugene Teo <eugeneteo () kernel sg>]

Heads-up. You might want to backport this if your kernel is affected. We 
are not requesting a CVE name for this as it does not affect any of our 
Red Hat supported kernels.

More info here:
http://patchwork.kernel.org/patch/83353/
https://bugzilla.redhat.com/show_bug.cgi?id=568621

Thanks, Eugene