vt: use /dev/vcs (not /dev/vcs0) in comment

Both /dev/vcs and /dev/vcs0 were in use in the past, but these days
/dev/vcs0 is mostly historical curiosity.

* "/dev/vcs" is the name that has always been in the Linux allocated
devices list.

* "vcs" is the device name in sysfs since Linux v2.6.12.

* MAKEDEV(1) in Debian used to create /dev/vcs0 only, but /dev/vcs was
  added in 1999: https://bugs.debian.org/45698

* MAKEDEV(1) in RedHat switched from /dev/vcs0 to /dev/vcs in 2000:

    * Fri Oct 20 2000 Nalin Dahyabhai <nalin@redhat.com>
      - change vcs0 to vcs (ditto for vcsa0)
Signed-off-by: Jakub Wilk <jwilk@jwilk.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/vt/vc_screen.c

 // SPDX-License-Identifier: GPL-2.0
 /*
  * Provide access to virtual console memory.
- * /dev/vcs0: the screen as it is being viewed right now (possibly scrolled)
+ * /dev/vcs: the screen as it is being viewed right now (possibly scrolled)
  * /dev/vcsN: the screen of /dev/ttyN (1 <= N <= 63)
  *            [minor: N]
  *