nfs: fix setting of ACLs on file creation.

nfs3_get_acl() tries to skip posix equivalent ACLs, but misinterprets
the return value of posix_acl_equiv_mode(). Fix it.

This is a regression introduced by
"nfs: use generic posix ACL infrastructure for v3 Posix ACLs"

CC: Christoph Hellwig <hch@infradead.org>
CC: linux-nfs@vger.kernel.org
CC: linux-fsdevel@vger.kernel.org

Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>