ida_simple_[get|remove] are wrappers anyways.

Also, use ida_alloc_min with the ns_ida as namespace
enumeration starts with 1.
Signed-off-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Keith Busch <kbusch@kernel.org>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>