Description of problem:
When starting a VM with preference with the PreferredStorageClassName field, we must specify dataVolumeTemplates[0].spec.pvc, this will also auto populate dataVolumeTemplates[0].spec.pvc.resource which conflict with dataVolumeTemplates[0].spec.storage.resources.requests.storage

Version-Release number of selected component (if applicable):
4.14.0

How reproducible:
100%

Steps to Reproduce:
1. Create VM with preference with PreferredStorageClassName
2. Add dataVolumeTemplates[0].spec.pvc.name to the VM spec
3.

Actual results:
The VMI fail to be created with conflict error of 2 resources fields defined

Expected results:
The VMI should be created

Additional info:
an example of the conflict fields:
dataVolumeTemplates:

• apiVersion: cdi.kubevirt.io/v1beta1
  kind: DataVolume
  metadata:
  creationTimestamp: null
  name: fedora
  spec:
  pvc:
  resources: {}
  storageClassName: nfs
  volumeName: volume-for-test
  sourceRef:
  kind: DataSource
  name: fedora
  namespace: openshift-virtualization-os-images
  storage:
  resources:
  requests:
  storage: "34087042032"