Make the mux always go through qemu_chr_fe_write, so that we'll get
the mutex for the underlying chardev.
Reviewed-by: NFam Zheng <famz@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: NLuiz Capitulino <lcapitulino@redhat.com>