jtag: fix error on TCL command "return" in jtag event handler

The TCL command "return" always returns error code JIM_RETURN, to
indicate that the effective error code and message are elsewhere.

In the current implementation, the caller of jtag's event only
checks for return code JIM_OK and considers any other value,
including JIM_RETURN, as an error condition.

It can be tested running openocd on a jtag target and adding a
jtag event "setup" with a single line "return", e.g.
	openocd -f board/ti_cc3200_launchxl.cfg \
	-c 'jtag configure cc32xx.cpu -event setup return'
to get the message:
	../src/jtag/core.c:1599: Error:
	in procedure 'jtag_init' called at file "../src/jtag/core.c",
	line 1599

Modify jtag_tap_handle_event() to detect the specific return value
of the "return" command and to test the real error code that is,
eventually, specified to the TCL "return" command.

Change-Id: I6d6febc15ef169638afffbffc1810e0b84fcf5c8
Reported-by: Tomas Vanek <[email protected]>
Signed-off-by: Antonio Borneo <[email protected]>
Reviewed-on: http:https://openocd.zylin.com/5199
Tested-by: jenkins
Reviewed-by: Tomas Vanek <[email protected]>

src/jtag/tcl.c

@@ -639,6 +639,7 @@ static int jim_newtap_cmd(Jim_GetOptInfo *goi)
 static void jtag_tap_handle_event(struct jtag_tap *tap, enum jtag_event e)
 {
  struct jtag_tap_event_action *jteap;
+ int retval;
 
  for (jteap = tap->event_action; jteap != NULL; jteap = jteap->next) {
  if (jteap->event != e)
@@ -649,7 +650,11 @@ static void jtag_tap_handle_event(struct jtag_tap *tap, enum jtag_event e)
  tap->dotted_name, e, nvp->name,
  Jim_GetString(jteap->body, NULL));
 
- if (Jim_EvalObj(jteap->interp, jteap->body) != JIM_OK) {
+ retval = Jim_EvalObj(jteap->interp, jteap->body);
+ if (retval == JIM_RETURN)
+ retval = jteap->interp->returnCode;
+
+ if (retval != JIM_OK) {
  Jim_MakeErrorMessage(jteap->interp);
  LOG_USER("%s", Jim_GetString(Jim_GetResult(jteap->interp), NULL));
  continue;