NFS: struct nfs_commit_info.lock must always point to inode->i_lock

NFS: struct nfs_commit_info.lock must always point to inode->i_lock

commit f4086a3d789dbe18949862276d83b8f49fce6d2f upstream.

Commit 411a99adffb4f (nfs: clear_request_commit while holding i_lock)
assumes that the nfs_commit_info always points to the inode->i_lock.
For historical reasons, that is not the case for O_DIRECT writes.

Cc: Weston Andros Adamson <dros@primarydata.com>
Fixes: 411a99adffb4f ("nfs: clear_request_commit while holding i_lock")
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>