virtio_pci: fix the common cfg map size

The function vp_modern_map_capability() takes the size parameter,
which corresponds to the size of virtio_pci_common_cfg. As a result,
this indicates the size of memory area to map.

Now the size is the size of virtio_pci_common_cfg, but some feature(such
as the _F_RING_RESET) needs the virtio_pci_modern_common_cfg, so this
commit changes the size to the size of virtio_pci_modern_common_cfg.

Cc: stable@vger.kernel.org
Fixes: 0b50cece ("virtio_pci: introduce helper to get/set queue reset")
Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Message-Id: <20231010031120.81272-3-xuanzhuo@linux.alibaba.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>