gpio: Handle deferred probing in of_find_gpio() properly

of_get_named_gpiod_flags() used directly in of_find_gpio() or indirectly
through of_find_spi_gpio() or of_find_regulator_gpio() can return
-EPROBE_DEFER. This gets overwritten by the subsequent of_find_*_gpio()
calls.

This patch fixes this by trying of_find_spi_gpio() or
of_find_regulator_gpio() only if deferred probing was not requested by
the previous of_get_named_gpiod_flags() call.

Fixes: 6a537d48 ("gpio: of: Support regulator nonstandard GPIO properties")
Fixes: c8582339 ("gpio: of: Support SPI nonstandard GPIO properties")
Signed-off-by: Chen-Yu Tsai <wens@csie.org>
[Augmented to fit with Maxime's patch]
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/gpiolib-of.c

@@ -263,7 +263,7 @@ struct gpio_desc *of_find_gpio(struct device *dev, const char *con_id,
 		desc = of_find_spi_gpio(dev, con_id, &of_flags);
 
 	/* Special handling for regulator GPIOs if used */
-	if (IS_ERR(desc))
+	if (IS_ERR(desc) && PTR_ERR(desc) != -EPROBE_DEFER)
 		desc = of_find_regulator_gpio(dev, con_id, &of_flags);
 
 	if (IS_ERR(desc))