RDMA/odp: Iterate over the whole rbtree directly

Instead of intersecting a full interval, just iterate over every element
directly. This is faster and clearer.

Link: https://lore.kernel.org/r/20190819111710.18440-3-leon@kernel.org


Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>