use eargf.

Reference: /n/sources/patch/applied/formateargf
Date: Fri May  9 17:17:32 CES 2008
Signed-off-by: quanstro@quanstro.net

--- /sys/src/cmd/disk/format.c	Fri May  9 17:17:18 2008
+++ /sys/src/cmd/disk/format.c	Fri May  9 17:17:17 2008
@@ -181,7 +181,7 @@
 	memmove(label, "CYLINDRICAL", sizeof(label));
 	ARGBEGIN {
 	case 'c':
-		clustersize = atoi(ARGF());
+		clustersize = atoi(EARGF(usage()));
 		break;
 	case 'd':
 		dos = 1;
@@ -191,7 +191,7 @@
 		fflag = 1;
 		break;
 	case 'l':
-		a = ARGF();
+		a = EARGF(usage());
 		n = strlen(a);
 		if(n > sizeof(label))
 			n = sizeof(label);
@@ -200,14 +200,14 @@
 			label[n++] = ' ';
 		break;
 	case 'b':
-		pbs = ARGF();
+		pbs = EARGF(usage());
 		writepbs = 1;
 		break;
 	case 'r':
-		nresrv = atoi(ARGF());
+		nresrv = atoi(EARGF(usage()));
 		break;
 	case 't':
-		type = ARGF();
+		type = EARGF(usage());
 		break;
 	case 'v':
 		chatty++;