vt: keyboard, union perm checks in vt_do_kdsk_ioctl

Do the permission check on a single place. That is where perm is really
checked.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Link: https://lore.kernel.org/r/20201029113222.32640-7-jslaby@suse.cz


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>