NFS: return error from decode_getfh in decode open

commit 01913b49cf1dc6409a07dd2a4cc6af2e77f3c410 upstream.

If decode_getfh failed, nfs4_xdr_dec_open would return 0 since the last
decode_* call must have succeeded.

Signed-off-by: Weston Andros Adamson <dros@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>