api: Fix vm.add-device argument type

The add_device() function, from the device manager code, takes a
DeviceConfig as a parameter, instead of a VmAddDevice.

The change was originally done as part of 34412c9b41 and it didn't
break Kata Containers because the VmAddDevice and DeviceConfig structs
share most of their fields, besides the optional for serialization
`pci_segment`, which is not used by the client yet.

Signed-off-by: Fabiano Fidêncio <fabiano.fidencio@intel.com>
Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>

vmm/src/api/openapi/cloud-hypervisor.yaml

@@ -185,7 +185,7 @@ paths:
         content:
           application/json:
             schema:
-              $ref: "#/components/schemas/VmAddDevice"
+              $ref: "#/components/schemas/DeviceConfig"
         required: true
       responses:
         200:
@@ -1077,17 +1077,6 @@ components:
           type: integer
           format: int64
 
-    VmAddDevice:
-      type: object
-      properties:
-        path:
-          type: string
-        iommu:
-          type: boolean
-          default: false
-        id:
-          type: string
-
     VmRemoveDevice:
       type: object
       properties: