nfs4_read_done returns zero on unhandled errors. nfs_readpage_result will
return on a negative tk_status without freeing the slot.
Call nfs4_sequence_free_slot on unhandled errors in nfs4_read_done.
Signed-off-by: NAndy Adamson <andros@netapp.com>
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>