handle visorchannel_signalinsert() errors in visorchipset.c

[selltc]

KanBoard-25159

This is in-response to GregKH's 8/21 email. We need to decide on a consistent and sensible way to handle signalinsert errors (rather than to ignore them), and implement it.

Here is an excerpt from Greg's email indicating the problem:

 >
 >      controlvm_init_response(&outmsg, p->pending_msg_hdr, response);
 >
 >      outmsg.cmd.device_change_state.bus_no = bus_no;
 >      outmsg.cmd.device_change_state.dev_no = dev_no;
 >      outmsg.cmd.device_change_state.state = response_state;
 >
 >      if (!visorchannel_signalinsert(controlvm_channel,
 >                                     CONTROLVM_QUEUE_REQUEST, &outmsg))
 >              return;

 Yet if we don't error, we return anyway?  {sigh}