virtio: pci: Fix an error handling path in vp_modern_probe()

If an error occurs after a successful pci_request_selected_regions() call,
it should be undone by a corresponding pci_release_selected_regions() call,
as already done in vp_modern_remove().

Fixes: fd502729 ("virtio-pci: introduce modern device module")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Message-Id: <237109725aad2c3c03d14549f777b1927c84b045.1648977064.git.christophe.jaillet@wanadoo.fr>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>