USB: usbtmc: prevent kernel-usb-infoleak

The syzbot reported a kernel-usb-infoleak in usbtmc_write,
we need to clear the structure before filling fields.

Fixes: 4ddc645f ("usb: usbtmc: Add ioctl for vendor specific write")
Reported-and-tested-by: syzbot+9d34f80f841e948c3fdb@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=9d34f80f841e948c3fdbSigned-off-by: Edward Adam Davis <eadavis@qq.com>
Cc: stable <stable@kernel.org>
Link: https://lore.kernel.org/r/tencent_9649AA6EC56EDECCA8A7D106C792D1C66B06@qq.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/class/usbtmc.c

@@ -754,7 +754,7 @@ static struct urb *usbtmc_create_urb(void)
 	if (!urb)
 		return NULL;
 
-	dmabuf = kmalloc(bufsize, GFP_KERNEL);
+	dmabuf = kzalloc(bufsize, GFP_KERNEL);
 	if (!dmabuf) {
 		usb_free_urb(urb);
 		return NULL;