nvme: initialize variable before logical OR'ing it

It is typically not good coding or secure coding practice
to logical OR a variable without an initialization value first.
Here on this line:

integrity.flags |= BLK_INTEGRITY_DEVICE_CAPABLE;

BLK_INTEGRITY_DEVICE_CAPABLE is being OR'ed to a member variable
never set to an initial value. This patch fixes that.

Signed-off-by: Jay Freyensee <james.p.freyensee@intel.com>
Reviewed-by: Ming Lin <ming.l@samsung.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>