media: mantis: prevent staying forever in a loop at IRQ

As warned by smatch:
	drivers/media/pci/mantis/mantis_uart.c:105 mantis_uart_work() warn: this loop depends on readl() succeeding

If something goes wrong at readl(), the logic will stay there
inside an IRQ code forever. This is not the nicest thing to
do :-)

So, add a timeout there, preventing staying inside the IRQ
for more than 10ms.
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

drivers/media/pci/mantis/mantis_uart.c

@@ -92,6 +92,7 @@ static void mantis_uart_work(struct work_struct *work)
 {
 	struct mantis_pci *mantis = container_of(work, struct mantis_pci, uart_work);
 	u32 stat;
+	unsigned long timeout;
 
 	stat = mmread(MANTIS_UART_STAT);
 
@@ -102,9 +103,15 @@ static void mantis_uart_work(struct work_struct *work)
 	 * MANTIS_UART_RXFIFO_DATA is only set if at least
 	 * config->bytes + 1 bytes are in the FIFO.
 	 */
+
+	/* FIXME: is 10ms good enough ? */
+	timeout = jiffies +  msecs_to_jiffies(10);
 	while (stat & MANTIS_UART_RXFIFO_DATA) {
 		mantis_uart_read(mantis);
 		stat = mmread(MANTIS_UART_STAT);
+
+		if (!time_is_after_jiffies(timeout))
+			break;
 	}
 
 	/* re-enable UART (RX) interrupt */