nvmet: allow identical cntlid_min and cntlid_max settings

When the user wants to restrict to only creating one controller,
they can set cntlid_min and cntlid_max to the same value.

Signed-off-by: Guixin Liu <kanie@linux.alibaba.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Keith Busch <kbusch@kernel.org>