NFSv4/pnfs: Replace pnfs_put_lseg_locked() with pnfs_put_lseg()

Now that we no longer hold the inode->i_lock when manipulating the
commit lists, it is safe to call pnfs_put_lseg() again.

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