Makefile: Fix the generation of locales

The -s option is only mandatory for the charmap,
else the filename is always empty and nothing
is generated.

Signed-off-by: Thierry Bultel <thierry.bultel@wanadoo.fr>
Acked-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>