nvme-core: use u16 type for ctrl->sqsize

In nvme_init_identify() when calculating submission queue size use u16
instead of int type in the min_t() since target variable ctrl->sqsize is
of type u16.

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