Make this WARNS=6 clean by just constifying two local char pointers.

usr.sbin/nghook/Makefile

@@ -4,6 +4,7 @@
 PROG=	nghook
 MAN=	nghook.8
 SRCS=	main.c
+WARNS=	6
 
 DPADD=	${LIBNETGRAPH}
 LDADD=	-lnetgraph

usr.sbin/nghook/main.c

@@ -71,7 +71,8 @@ int
 main(int ac, char *av[])
 {
 	struct ngm_connect ngc;
-	char   *path = NULL, *hook = DEFAULT_HOOKNAME;
+	const char *path = NULL;
+	const char *hook = DEFAULT_HOOKNAME;
 	int     csock, dsock;
 	int     asciiFlag = 0;
 	int     loopFlag = 0;