nfs: Use ida_simple API

Allocate the owner_id when we allocate the state and free it when we free
the state.  That lets us get rid of a gnarly ida_pre_get() / ida_get_new()
loop.

Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>