nvme: delete an unnecessary declaration

The nvme_put_ctrl() is implemented earlier as an inline function so
this declaration isn't required.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>