NFS: nfs_inode_return_delegation() should always flush dirty data

The assumption is that if you are in a situation where you need to
return the delegation, then you should probably stop caching the
data anyway.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

diff --cc fs/nfs/delegation.c
Simple merge

diff --cc fs/nfs/delegation.h
Simple merge