staging/wilc1000: make symbols static if possible

All symbols that are only referenced in the file that defines
them can be declared 'static' to avoid namespace pollution,
to produce better object code, and to make the source more
readable.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>