tty: vt: consolemap: Demote weakly documented function header

tty: vt: consolemap: Demote weakly documented function header

Fixes the following W=1 kernel build warning(s):

 drivers/tty/vt/consolemap.c:739: warning: Function parameter or member 'ct' not described in 'con_get_unimap'
 drivers/tty/vt/consolemap.c:739: warning: Function parameter or member 'uct' not described in 'con_get_unimap'
 drivers/tty/vt/consolemap.c:739: warning: Function parameter or member 'list' not described in 'con_get_unimap'

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jirislaby@kernel.org>
Cc: Jakub Jelinek <jj@ultra.linux.cz>
Cc: Stanislav Voronyi <stas@cnti.uanet.kharkov.ua>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20201104193549.4026187-10-lee.jones@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>