pnfs: set NFS_IOHDR_REDO in pnfs_read_resend_pnfs

Like other resend paths, mark the (old) hdr as NFS_IOHDR_REDO. This
ensures the hdr completion function will not count the (old) hdr
as good bytes.

Also, vector the error back through the hdr->task.tk_status like other
retry calls.

This fixes a bug with the FlexFiles layout where libaio was reporting more
bytes read than requested.

Signed-off-by: Weston Andros Adamson <dros@primarydata.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>