nvme: set 0 capacity if namespace block size exceeds PAGE_SIZE

If our target exposed a namespace with a block size that is greater
than PAGE_SIZE, set 0 capacity on the namespace as we do not support it.

This issue encountered when the nvmet namespace was backed by a tempfile.

Signed-off-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>