Clean up tab damage and comments.  Replace "file_offset" with more commonly
used "pos".

Test plan:
Compile with CONFIG_NFS and CONFIG_NFS_DIRECTIO enabled.
Signed-off-by: NChuck Lever <cel@netapp.com>
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>