net/widentd: disable -Werror

On gcc, this warning is given:

widentd.c: In function 'main':
widentd.c:194:3: error: 'memset' used with constant zero length parameter;

this could be due to transposed parameters
[-Werror=memset-transposed-args]
 memset(buff, sizeof(buff), 0);
 ^

Removing -Werror is blanket-approved. This is another port that uses
<bsd.prog.mk> instead of providing an independent makefile, so the
-Werror is coming from the system build framework.