NVMe: cq_vector should be signed

This was inadvertently dropped from an earlier commit, otherwise
the check against cq_vector == -1 to prevent double free doesn't
make any sense.

Fixes: 2b25d981790b
Signed-off-by: Jens Axboe <axboe@fb.com>

drivers/block/nvme-core.c

@@ -106,7 +106,7 @@ struct nvme_queue {
 	dma_addr_t cq_dma_addr;
 	u32 __iomem *q_db;
 	u16 q_depth;
-	u16 cq_vector;
+	s16 cq_vector;
 	u16 sq_head;
 	u16 sq_tail;
 	u16 cq_head;