greybus: don't assume subdevs are valid

Most of the disconnect routines for the "subdevs" of a module
blindly assume that initialization of the subdev was successful.

Fix this by checking for null pointers.
Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>

drivers/staging/greybus/battery-gb.c

@@ -135,6 +135,8 @@ void gb_battery_disconnect(struct gb_module *gmod)
 	struct gb_battery *gb;
 
 	gb = gmod->gb_battery;
+	if (!gb)
+		return;
 
 	power_supply_unregister(&gb->bat);
 

drivers/staging/greybus/gpio-gb.c

@@ -92,6 +92,8 @@ void gb_gpio_disconnect(struct gb_module *gmod)
 	int retval;
 
 	gb_gpio_dev = gmod->gb_gpio_dev;
+	if (!gb_gpio_dev)
+		return;
 
 	retval = gpiochip_remove(&gb_gpio_dev->chip);
 	kfree(gb_gpio_dev);

drivers/staging/greybus/i2c-gb.c

@@ -121,6 +121,8 @@ void gb_i2c_disconnect(struct gb_module *gmod)
 	struct gb_i2c_device *gb_i2c_dev;
 
 	gb_i2c_dev = gmod->gb_i2c_dev;
+	if (!gb_i2c_dev)
+		return;
 	i2c_del_adapter(gb_i2c_dev->adapter);
 	kfree(gb_i2c_dev->adapter);
 	kfree(gb_i2c_dev);

drivers/staging/greybus/sdio-gb.c

@@ -71,8 +71,10 @@ void gb_sdio_disconnect(struct gb_module *gmod)
 	struct gb_sdio_host *host;
 
 	host = gmod->gb_sdio_host;
-	mmc = host->mmc;
+	if (!host)
+		return;
 
+	mmc = host->mmc;
 	mmc_remove_host(mmc);
 	mmc_free_host(mmc);
 }