lightnvm: print error when target is not found

If userspace requests target to be removed, nvm_remove_tgt() will
iterate the nvm_devices to find out the given target, but if not
found, then it should print out an error.
Signed-off-by: Minwoo Im <minwoo.im.dev@gmail.com>
Updated output string and patch description.
Signed-off-by: Matias Bjørling <mb@lightnvm.io>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/lightnvm/core.c

@@ -495,8 +495,11 @@ static int nvm_remove_tgt(struct nvm_ioctl_remove *remove)
 	}
 	up_read(&nvm_lock);
 
-	if (!t)
+	if (!t) {
+		pr_err("failed to remove target %s\n",
+				remove->tgtname);
 		return 1;
+	}
 
 	__nvm_remove_target(t, true);
 	kref_put(&dev->ref, nvm_free);