serial: 8250_pci1xxxx: partially revert off by one patch

I was reviewing this code again and I realized I made a mistake here.
It should have been > instead of >=.  The subtract ensures that we
don't go out of bounds.  My patch meant that we don't read the last
chunk of the buffer.

Fixes: 86ee55e ("serial: 8250_pci1xxxx: fix off by one in pci1xxxx_process_read_data()")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Link: https://lore.kernel.org/r/bd6fb361-bbb9-427d-90e8-a5df4de76221@moroto.mountain
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: Dan Carpenter

drivers/tty/serial/8250/8250_pci1xxxx.c

@@ -302,7 +302,7 @@ static void pci1xxxx_process_read_data(struct uart_port *port,
 	 * to read, the data is received one byte at a time.
 	 */
 	while (valid_burst_count--) {
-		if (*buff_index >= (RX_BUF_SIZE - UART_BURST_SIZE))
+		if (*buff_index > (RX_BUF_SIZE - UART_BURST_SIZE))
 			break;
 		burst_buf = (u32 *)&rx_buff[*buff_index];
 		*burst_buf = readl(port->membase + UART_RX_BURST_FIFO);