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/char/hvc_console.c b/drivers/char/hvc_console.c
index 94e7e3c..d97779e 100644
--- a/drivers/char/hvc_console.c
+++ b/drivers/char/hvc_console.c
@@ -552,7 +552,7 @@
 	struct hvc_struct *hp = tty->driver_data;
 
 	if (!hp)
-		return -1;
+		return 0;
 	return hp->n_outbuf;
 }