hw/virtio/vhost-user:Remove dead assignment in scrub_shadow_regions()

Clang static code analyzer show warning:
hw/virtio/vhost-user.c:606:9: warning: Value stored to 'mr' is never read
        mr = vhost_user_get_mr_data(reg->userspace_addr, &offset, &fd);
        ^    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Reported-by: Euler Robot <[email protected]>
Signed-off-by: Chen Qun <[email protected]>
Reviewed-by: Raphael Norwitz <[email protected]>
Reviewed-by: Michael S. Tsirkin <[email protected]>
Message-Id: <[email protected]>
Signed-off-by: Laurent Vivier <[email protected]>

hw/virtio/vhost-user.c

@@ -603,7 +603,7 @@ static void scrub_shadow_regions(struct vhost_dev *dev,
      */
     for (i = 0; i < dev->mem->nregions; i++) {
         reg = &dev->mem->regions[i];
-        mr = vhost_user_get_mr_data(reg->userspace_addr, &offset, &fd);
+        vhost_user_get_mr_data(reg->userspace_addr, &offset, &fd);
         if (fd > 0) {
             ++fd_num;
         }