dj(1), intcmp(1), mm(1), npc(1), scrut(1), str(1): make usage function consistent

src/dj.c

@@ -146,11 +146,13 @@ parse(char *s) {
 }
 
 static int
-usage(char *s) {
-	fprintf(
-		stderr, "Usage: %s [-Hn] [-a byte] [-c count]\n"
+usage(char *argv0) {
+	(void)fprintf(
+		stderr,
+		"Usage: %s [-Hn] [-a byte] [-c count]\n"
 		"\t[-i file] [-b block_size] [-s offset]\n"
-		"\t[-o file] [-B block_size] [-S offset]\n", s
+		"\t[-o file] [-B block_size] [-S offset]\n",
+		argv0
 	);
 
 	return EX_USAGE;