vcs: invoke the vt update callback when /dev/vcs* is written to

A notifier chain is called whenever the vt code modifies a terminal
content, except for one case which is when the modification comes
through writes to /dev/vcs* devices.  Let's add the missing notifier
invocation at the end of vcs_write() for that case too.

Signed-off-by: Nicolas Pitre <nicolas.pitre@canonical.com>
Cc: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>