tty: vt/Makefile: set the variables to static

In the file drivers/tty/vt/defkeymap.c generated by command
loadkeys --mktable defkeymap.map > defkeymap.c
the 6 variables: shift_map, altgr_map, ctrl_map, shift_ctrl_map, alt_map,
and ctrl_alt_map should be static because they are used only in this file.
There is no reason to remove the static by sed command.
Signed-off-by: Cong Ding <dinggnu@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>