ktest: Fix child exit code processing

commit 32677207 upstream.

The child_exit errno needs to be shifted by 8 bits to compare against the
return values for the bisect variables.

Fixes: c5dacb88 ("ktest: Allow overriding bisect test results")
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

tools/testing/ktest/ktest.pl

@@ -2445,7 +2445,7 @@ sub do_run_test {
     }
 
     waitpid $child_pid, 0;
-    $child_exit = $?;
+    $child_exit = $? >> 8;
 
     if (!$bug && $in_bisect) {
 	if (defined($bisect_ret_good)) {