mmc: slot-gpio: Fix missing assignment to ctx->ro_gpio

mmc_gpio_request_ro() doesn't store the requested gpio in ctx->ro_gpio.
As a result, subsequent calls to mmc_gpio_get_ro() will always fail
with -ENOSYS because the gpio number isn't available to that function.

Cc: stable <stable@vger.kernel.org>
Acked-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Chris Ball <cjb@laptop.org>

drivers/mmc/core/slot-gpio.c

@@ -100,7 +100,13 @@ int mmc_gpio_request_ro(struct mmc_host *host, unsigned int gpio)
 
 	ctx = host->slot.handler_priv;
 
-	return gpio_request_one(gpio, GPIOF_DIR_IN, ctx->ro_label);
+	ret = gpio_request_one(gpio, GPIOF_DIR_IN, ctx->ro_label);
+	if (ret < 0)
+		return ret;
+
+	ctx->ro_gpio = gpio;
+
+	return 0;
 }
 EXPORT_SYMBOL(mmc_gpio_request_ro);