serial: 8250_omap: check how many bytes were injected

The function tty_insert_flip_string() returns an int and as such it
might fail. So the result is that I kindly asked to insert 48 bytes and
the function only insterted 32.
I have no idea what to do with the remaining 16 so I think dropping them
is the only option. I also increase the buf_overrun counter so userpace
has a clue that we lost bytes.
Signed-off-by: NSebastian Andrzej Siewior <bigeasy@linutronix.de>
Tested-by: NSekhar Nori <nsekhar@ti.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/8250/8250_omap.c

@@ -726,6 +726,7 @@ static void __dma_rx_do_complete(struct uart_8250_port *p, bool error)
 	struct dma_tx_state     state;
 	int                     count;
 	unsigned long		flags;
+	int			ret;
 
 	dma_sync_single_for_cpu(dma->rxchan->device->dev, dma->rx_addr,
 				dma->rx_size, DMA_FROM_DEVICE);
@@ -741,8 +742,10 @@ static void __dma_rx_do_complete(struct uart_8250_port *p, bool error)
 
 	count = dma->rx_size - state.residue;
 
-	tty_insert_flip_string(tty_port, dma->rx_buf, count);
-	p->port.icount.rx += count;
+	ret = tty_insert_flip_string(tty_port, dma->rx_buf, count);
+
+	p->port.icount.rx += ret;
+	p->port.icount.buf_overrun += count - ret;
 unlock:
 	spin_unlock_irqrestore(&priv->rx_dma_lock, flags);