selftests/x86/fsgsbase: Reap a forgotten child

The ptrace() test forgot to reap its child.  Reap it.
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/e7700a503f30e79ab35a63103938a19893dbeff2.1598461151.git.luto@kernel.org

tools/testing/selftests/x86/fsgsbase.c

@@ -517,6 +517,9 @@ static void test_ptrace_write_gsbase(void)
 
 END:
 	ptrace(PTRACE_CONT, child, NULL, NULL);
+	wait(&status);
+	if (!WIFEXITED(status))
+		printf("[WARN]\tChild didn't exit cleanly.\n");
 }
 
 int main()