Use _PATH_DEV, not "/dev/"

Make init(8) call login_fbtab() correctly.

src/lib/libutil/login_fbtab.c

@@ -66,6 +66,7 @@
 #include <errno.h>
 #include <dirent.h>
 #include <unistd.h>
+#include <paths.h>
 
 #include "util.h"
 
@@ -96,7 +97,7 @@ login_fbtab(tty, uid, gid)
 			*cp = 0;	/* strip comment */
 		if ((cp = devname = strtok(buf, WSPACE)) == 0)
 			continue;	/* empty or comment */
-		if (strncmp(devname, "/dev/", sizeof("/dev/")-1) != 0 ||
+		if (strncmp(devname, _PATH_DEV, sizeof(_PATH_DEV) - 1) != 0 ||
 		    (cp = strtok((char *) 0, WSPACE)) == 0 ||
 		    *cp != '0' ||
 		    sscanf(cp, "%o", &prot) == 0 ||
@@ -107,7 +108,7 @@ login_fbtab(tty, uid, gid)
 			    cp ? cp : "(null)");
 			continue;
 		}
-		if (strcmp(devname + 5, tty) == 0)
+		if (strcmp(devname + sizeof(_PATH_DEV) - 1, tty) == 0)
 			for (cp = strtok(cp, ":"); cp; cp = strtok(NULL, ":"))
 				login_protect(table, cp, prot, uid, gid);
 	}