RDMA: Provide safe ib_alloc_device() function

All callers to ib_alloc_device() provide a larger size than struct
ib_device and rely on the fact that struct ib_device is embedded in their
driver specific structure as the first member.

Provide a safer variant of ib_alloc_device() that checks and enforces this
approach to make sure the drivers are using it right.

Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

drivers/infiniband/hw/qedr/main.c

@@ -853,7 +853,7 @@ static struct qedr_dev *qedr_add(struct qed_dev *cdev, struct pci_dev *pdev,
 	struct qedr_dev *dev;
 	int rc = 0;
 
-	dev = (struct qedr_dev *)ib_alloc_device(sizeof(*dev));
+	dev = ib_alloc_device(qedr_dev, ibdev);
 	if (!dev) {
 		pr_err("Unable to allocate ib device\n");
 		return NULL;