serial: 8250_omap: fix a timeout loop condition

This loop ends on -1 so the error message will never be printed.

Fixes: 4bcf59a5 ("serial: 8250: 8250_omap: Account for data in flight during DMA teardown")
Reviewed-by: Alexander Sverdlin <alexander.sverdlin@gmail.com>
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Link: https://lore.kernel.org/r/YIpd+kOpXKMpEXPf@mwandaSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

@@ -813,7 +813,7 @@ static void __dma_rx_do_complete(struct uart_8250_port *p)
 			       poll_count--)
 				cpu_relax();
 
-			if (!poll_count)
+			if (poll_count == -1)
 				dev_err(p->port.dev, "teardown incomplete\n");
 		}
 	}