vfio/pci: Fix mistakenly deleted "vdev->num_regions"

virt inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I6LQMC


CVE: NA

---------------------

In commit 6f5013f4, the 'vdev->num_regions' was deleted by mistake.

Fixes: 6f5013f4 (Revert "vfio/pci: Add framework for custom interrupt indices")
Signed-off-by: Kunkun Jiang <jiangkunkun@huawei.com>