tty: fix chars_in_buffers

This function does not have an error return and returning an error is
instead interpreted as having a lot of pending bytes.

Reported by Jeff Harris who provided a list of some of the remaining
offenders.

Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c
index 5b15d9d..e1f8941 100644
--- a/drivers/usb/class/cdc-acm.c
+++ b/drivers/usb/class/cdc-acm.c
@@ -750,7 +750,7 @@
 {
 	struct acm *acm = tty->driver_data;
 	if (!ACM_READY(acm))
-		return -EINVAL;
+		return 0;
 	/*
 	 * This is inaccurate (overcounts), but it works.
 	 */
diff --git a/drivers/usb/serial/mos7720.c b/drivers/usb/serial/mos7720.c
index bfc5ce0..ccd4dd3 100644
--- a/drivers/usb/serial/mos7720.c
+++ b/drivers/usb/serial/mos7720.c
@@ -521,7 +521,7 @@
 	mos7720_port = usb_get_serial_port_data(port);
 	if (mos7720_port == NULL) {
 		dbg("%s:leaving ...........", __func__);
-		return -ENODEV;
+		return 0;
 	}
 
 	for (i = 0; i < NUM_URBS; ++i) {
diff --git a/drivers/usb/serial/ti_usb_3410_5052.c b/drivers/usb/serial/ti_usb_3410_5052.c
index 14971a9..3bc609f 100644
--- a/drivers/usb/serial/ti_usb_3410_5052.c
+++ b/drivers/usb/serial/ti_usb_3410_5052.c
@@ -727,7 +727,7 @@
 	dbg("%s - port %d", __func__, port->number);
 
 	if (tport == NULL)
-		return -ENODEV;
+		return 0;
 
 	spin_lock_irqsave(&tport->tp_lock, flags);
 	room = ti_buf_space_avail(tport->tp_write_buf);
@@ -748,7 +748,7 @@
 	dbg("%s - port %d", __func__, port->number);
 
 	if (tport == NULL)
-		return -ENODEV;
+		return 0;
 
 	spin_lock_irqsave(&tport->tp_lock, flags);
 	chars = ti_buf_data_avail(tport->tp_write_buf);