fix a regression in atomic_open()

open("/foo/no_such_file", O_RDONLY | O_CREAT) on should fail with
EACCES when /foo is not writable; failing with ENOENT is obviously
wrong.  That got broken by a braino introduced when moving the
creat_error logics from atomic_open() to lookup_open().  Easy to
fix, fortunately.
Spotted-by: N"Yan, Zheng" <ukernel@gmail.com>
Tested-by: N"Yan, Zheng" <ukernel@gmail.com>
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

fs/namei.c

@@ -2995,9 +2995,13 @@ static int atomic_open(struct nameidata *nd, struct dentry *dentry,
 			}
 			if (*opened & FILE_CREATED)
 				fsnotify_create(dir, dentry);
-			path->dentry = dentry;
-			path->mnt = nd->path.mnt;
-			return 1;
+			if (unlikely(d_is_negative(dentry))) {
+				error = -ENOENT;
+			} else {
+				path->dentry = dentry;
+				path->mnt = nd->path.mnt;
+				return 1;
+			}
 		}
 	}
 	dput(dentry);