Use explicit casts when dumping config data

GCC pointes out that we're in a gray area

second/cfg.c: In function ‘cfg_reset’:
second/cfg.c:437: warning: format ‘%s’ expects type ‘char *’, but argument 3 has type ‘void *’
second/cfg.c:442: warning: format ‘%s’ expects type ‘char *’, but argument 3 has type ‘void *’

Signed-off-by: Tony Breeds <tony@bakeyournoodle.com>