tty/serial: at91: fix error handling in atmel_serial_probe()

-EDEFER error wasn't handle properly by atmel_serial_probe().
As an example, when atmel_serial_probe() is called for the first time, we pass
the test_and_set_bit() test to check whether the port has already been
initalized. Then we call atmel_init_port(), which may return -EDEFER, possibly
returned before by clk_get(). Consequently atmel_serial_probe() used to return
this error code WITHOUT clearing the port bit in the "atmel_ports_in_use" mask.
When atmel_serial_probe() was called for the second time, it used to fail on
the test_and_set_bit() function then returning -EBUSY.

When atmel_serial_probe() fails, this patch make it clear the port bit in the
"atmel_ports_in_use" mask, if needed, before returning the error code.
Signed-off-by: Cyrille Pitchen <cyrille.pitchen@atmel.com>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Cc: <stable@vger.kernel.org> # 3.12+
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/atmel_serial.c

@@ -2565,7 +2565,7 @@ static int atmel_serial_probe(struct platform_device *pdev)
 
 	ret = atmel_init_port(port, pdev);
 	if (ret)
-		goto err;
+		goto err_clear_bit;
 
 	if (!atmel_use_pdc_rx(&port->uart)) {
 		ret = -ENOMEM;
@@ -2628,6 +2628,8 @@ static int atmel_serial_probe(struct platform_device *pdev)
 		clk_put(port->clk);
 		port->clk = NULL;
 	}
+err_clear_bit:
+	clear_bit(port->uart.line, atmel_ports_in_use);
 err:
 	return ret;
 }