nvme-core: get rid of the extra space

Remove the extra space in the nvme_free_cels() when calling
xa_for_each loop which is not a common practice
(except drivers/infiniband/core/ not sure why).

Signed-off-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>