lightnvm: propagate device_add() error code

device_add() may fail, and all callers are supposed to check the
return value, but one new user in lightnvm doesn't:

drivers/lightnvm/sysfs.c: In function 'nvm_sysfs_register_dev':
drivers/lightnvm/sysfs.c:184:2: error: ignoring return value of 'device_add',
  declared with attribute warn_unused_result [-Werror=unused-result]

This changes the caller to propagate any error codes, which avoids
the warning.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Fixes: 38c9e260b9f9 ("lightnvm: expose device geometry through sysfs")
Signed-off-by: Matias Bjørling <m@bjorling.me>
Signed-off-by: Jens Axboe <axboe@fb.com>

drivers/lightnvm/lightnvm.h

@@ -24,7 +24,7 @@
 #include <linux/lightnvm.h>
 
 /* core -> sysfs.c */
-int nvm_sysfs_register_dev(struct nvm_dev *);
+int __must_check nvm_sysfs_register_dev(struct nvm_dev *);
 void nvm_sysfs_unregister_dev(struct nvm_dev *);
 int nvm_sysfs_register(void);
 void nvm_sysfs_unregister(void);

drivers/lightnvm/sysfs.c

@@ -174,6 +174,8 @@ static struct device_type nvm_type = {
 
 int nvm_sysfs_register_dev(struct nvm_dev *dev)
 {
+	int ret;
+
 	if (!dev->parent_dev)
 		return 0;
 
@@ -181,11 +183,12 @@ int nvm_sysfs_register_dev(struct nvm_dev *dev)
 	dev_set_name(&dev->dev, "%s", dev->name);
 	dev->dev.type = &nvm_type;
 	device_initialize(&dev->dev);
-	device_add(&dev->dev);
+	ret = device_add(&dev->dev);
 
+	if (!ret)
 		blk_mq_register_dev(&dev->dev, dev->q);
 
-	return 0;
+	return ret;
 }
 
 void nvm_sysfs_unregister_dev(struct nvm_dev *dev)