homework-quota: pass the right error variable

(cherry picked from commit 2c30973)
(cherry picked from commit a2e7aac)
(cherry picked from commit 5de929e)

Author: dtardon

src/home/homework-quota.c

@@ -113,7 +113,7 @@ int home_update_quota_auto(UserRecord *h, const char *path) {
 
                 r = btrfs_is_subvol(path);
                 if (r < 0)
-                        return log_error_errno(errno, "Failed to test if %s is a subvolume: %m", path);
+                        return log_error_errno(r, "Failed to test if %s is a subvolume: %m", path);
                 if (r == 0)
                         return log_error_errno(SYNTHETIC_ERRNO(ENOTTY), "Directory %s is not a subvolume, cannot apply quota.", path);