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: NSunad Bhandary S <sunad.s@samsung.com>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NJens Axboe <axboe@fb.com>