mmc: cd-gpio: protect against NULL context in mmc_cd_gpio_free()

Do not oops, even if mmc_cd_gpio_free() is mistakenly called on a driver
cleanup path, even though a previous call to mmc_cd_gpio_request() failed.
Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
[stable@: please apply to 3.3-stable]
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Chris Ball <cjb@laptop.org>

drivers/mmc/core/cd-gpio.c

@@ -73,6 +73,9 @@ void mmc_cd_gpio_free(struct mmc_host *host)
 {
 	struct mmc_cd_gpio *cd = host->hotplug.handler_priv;
 
+	if (!cd)
+		return;
+
 	free_irq(host->hotplug.irq, host);
 	gpio_free(cd->gpio);
 	kfree(cd);