variable 'stat' set but not used [-Wunused-but-set-variable]

[sandrobonazzola]

While building the package, seen this warning from the compiler.

yajl_ext.c: In function 'rb_yajl_parser_parse':
yajl_ext.c:471:17: warning: variable 'stat' set but not used [-Wunused-but-set-variable]
yajl_status stat;

Probably not harming but also seems to be safe and easy to fix.