gpio: pcf857x: Fix missing first interrupt

commit a8002a35935aaefcd6a42ad3289f62bab947f2ca upstream.

If no n_latch value will be provided at driver probe then all pins will
be used as an input:

    gpio->out = ~n_latch;

In that case initial state for all pins is "one":

    gpio->status = gpio->out;

So if pcf857x IRQ happens with change pin value from "zero" to "one"
then we miss it, because of "one" from IRQ and "one" from initial state
leaves corresponding pin unchanged:
change = (gpio->status ^ status) & gpio->irq_enabled;

The right solution will be to read actual state at driver probe.

Cc: stable@vger.kernel.org
Fixes: 6e20a0a429bd ("gpio: pcf857x: enable gpio_to_irq() support")
Signed-off-by: Maxim Kiselev <bigunclemax@gmail.com>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/gpio/gpio-pcf857x.c

@@ -332,7 +332,7 @@ static int pcf857x_probe(struct i2c_client *client,
 	 * reset state.  Otherwise it flags pins to be driven low.
 	 */
 	gpio->out = ~n_latch;
-	gpio->status = gpio->out;
+	gpio->status = gpio->read(gpio->client);
 
 	/* Enable irqchip if we have an interrupt */
 	if (client->irq) {