vhost_vdpa: unset vq irq before freeing irq

vhost_vdpa: unset vq irq before freeing irq

Currently we unset vq irq after freeing irq and that will result in
error messages:

  pi_update_irte: failed to update PI IRTE
  irq bypass consumer (token 000000005a07a12b) unregistration fails: -22

This patch solves this.

Signed-off-by: Wu Zongyong <wuzongyong@linux.alibaba.com>
Link: https://lore.kernel.org/r/02637d38dcf4e4b836c5b3a65055fe92bf812b3b.1631687872.git.wuzongyong@linux.alibaba.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>