kfdtest: Fix the childStatus is 0x7f error for KFDDBGTest.HitMemoryViolation

For the case parent goes faster then child, and child hasn't call the second
raise(SIGSTOP), then parent's "waitpid(childPid, &childStatus, 0)" will return,
and the childStatus will be 0x137f, which is SIGSTOP signal id.

Signed-off-by: Emily Deng <Emily.Deng@amd.com>

libhsakmt/tests/kfdtest/src/KFDDBGTest.cpp

@@ -599,6 +599,9 @@ TEST_F(KFDDBGTest, HitMemoryViolation) {
                     break;
                 }
             }
+            waitpid(childPid, &childStatus, 0);
+            while (!WIFSTOPPED(childStatus));
+
             // Assume tracee queue has died and halted process
             ptrace(PTRACE_CONT, childPid, NULL, NULL);