aufs: bugfix, retval from au_pin() call in au_file_refresh_by_inode()

Simply it is a bug to call au_unpin() when the precedding au_pin()
returns an error.
To be honest, I was very surprised that this bug was born in aufs1 era
and lived very long time.

Signed-off-by: J. R. Okajima <hooanon05@yahoo.co.jp>
Merge remote branch 'aufs3-standalone/aufs3.2/00base' into aufs3.2/10static
Merge branch 'aufs3.2/10static' into aufs3.2/11proc_map
Merge branch 'aufs3.2/11proc_map' into aufs3.2/18public
aufs: tiny, new copy-up wrapper with h_open_pre/post()

It is possible to add a new copy-up flag AuCpup_HOPEN or something, but
I choose another way. It is required to add a new parameter to specify
the branch index, but I don't think it a good idea to add one more
parameter to au_sio_cpup_simple().

The behaviour doesn't change.

Signed-off-by: J. R. Okajima <hooanon05@yahoo.co.jp>
Merge remote branch 'aufs3-standalone/aufs3.2/00base' into aufs3.2/10static
Merge branch 'aufs3.2/10static' into aufs3.2/11proc_map
Merge branch 'aufs3.2/11proc_map' into aufs3.2/18public