vhost_vdpa: don't setup irq offloading when irq_num < 0

vhost_vdpa: don't setup irq offloading when irq_num < 0

[ Upstream commit cce0ab2b2a39072d81f98017f7b076f3410ef740 ]

When irq number is negative(e.g., -EINVAL), the virtqueue
may be disabled or the virtqueues are sharing a device irq.
In such case, we should not setup irq offloading for a virtqueue.

Signed-off-by: Zhu Lingshan <lingshan.zhu@intel.com>
Link: https://lore.kernel.org/r/20220222115428.998334-3-lingshan.zhu@intel.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>