eliminate arbitrary limit on devctl writes

Reference: /n/atom/patch/applied/usbdevctllimits
Date: Tue Mar 11 09:53:59 CET 2014
Signed-off-by: quanstro@quanstro.net

--- /sys/src/cmd/usb/lib/dev.c	Tue Mar 11 09:53:31 2014
+++ /sys/src/cmd/usb/lib/dev.c	Tue Mar 11 09:53:31 2014
@@ -52,7 +52,7 @@
 		mode = "w";
 	snprint(name, sizeof(name), "/dev/usb/ep%d.%d", d->id, id);
 	if(access(name, AEXIST) == 0){
-		dprint(2, "%s: %s already exists; trying to open\n", argv0, name);
+		dprint(2, "%s: %s already exists; trying to open mode %s\n", argv0, name, mode);
 		epd = opendev(name);
 		if(epd != nil)
 			epd->maxpkt = ep->maxpkt;	/* guess */
@@ -481,12 +481,14 @@
 int
 devctl(Dev *dev, char *fmt, ...)
 {
-	char buf[128];
+	char *s;
+	int r;
 	va_list arg;
-	char *e;
 
 	va_start(arg, fmt);
-	e = vseprint(buf, buf+sizeof(buf), fmt, arg);
+	s = vsmprint(fmt, arg);
 	va_end(arg);
-	return write(dev->cfd, buf, e-buf);
+	r = write(dev->cfd, s, strlen(s));
+	free(s);
+	return r;
 }