We will catch the bellow error report while try to delete compare object
by qmp command:
chardev/char-io.c:91: io_watch_poll_finalize: Assertion `iwp->src == ((void *)0)' failed.

This is caused by failing to remove the right fd been watched while
call qemu_chr_fe_set_handlers();

Fix it by pass the worker_context parameter to qemu_chr_fe_set_handlers().
Signed-off-by: Nzhanghailiang <zhang.zhanghailiang@huawei.com>
Reviewed-by: NZhang Chen <zhangchen.fnst@cn.fujitsu.com>
Signed-off-by: NJason Wang <jasowang@redhat.com>