NVMe: Fix removal in case of active namespace list scanning method

In case of the active namespace list scanning method, a namespace that
is detached is not removed from the host if it was the last entry in
the list. Fix this by adding a scan to validate namespaces greater than
the value of prev.

This also handles the case of removing namespaces whose value exceed
the device's reported number of namespaces.

Signed-off-by: Sunad Bhandary S <sunad.s@samsung.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>