virtio_net: Fix memory leak in virtnet_rx_mod_work

virtio_net: Fix memory leak in virtnet_rx_mod_work

The pointer delcaration was missing the __free(kfree).

Fixes: ff7c7d9f5261 ("virtio_net: Remove command data from control_buf")
Reported-by: Jens Axboe <axboe@kernel.dk>
Closes: https://lore.kernel.org/netdev/0674ca1b-020f-4f93-94d0-104964566e3f@kernel.dk/
Signed-off-by: Daniel Jurgens <danielj@nvidia.com>
Tested-by: Jens Axboe <axboe@kernel.dk>
Reviewed-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Link: https://lore.kernel.org/r/20240509183634.143273-1-danielj@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>