virtio-vdpa: Fix cpumask memory leak in virtio_vdpa_find_vqs()

Free the cpumask allocated by create_affinity_masks() before returning
from the function.

Fixes: 3dad5682 ("virtio-vdpa: Support interrupt affinity spreading mechanism")
Signed-off-by: Gal Pressman <gal@nvidia.com>
Reviewed-by: Dragos Tatulea <dtatulea@nvidia.com>
Message-Id: <20230726191036.14324-1-dtatulea@nvidia.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Reviewed-by: Xie Yongji <xieyongji@bytedance.com>