fastboot: avoid printing invalid data

There is no guarantee that commands are null-terminated in the USB
request buffer, so limit the length of data that is printed.

Signed-off-by: John Keeping <john@metanate.com>
Tested-by: Steve Rae <steve.rae@raedomain.com>
diff --git a/drivers/usb/gadget/f_fastboot.c b/drivers/usb/gadget/f_fastboot.c
index aecee7f..199621d 100644
--- a/drivers/usb/gadget/f_fastboot.c
+++ b/drivers/usb/gadget/f_fastboot.c
@@ -718,7 +718,7 @@
 	}
 
 	if (!func_cb) {
-		error("unknown command: %s", cmdbuf);
+		error("unknown command: %.*s", req->actual, cmdbuf);
 		fastboot_tx_write_str("FAILunknown command");
 	} else {
 		if (req->actual < req->length) {