Fix typo.

Change use of new_ to old_ to save the old sigaction data. This hasn't
caused any issues, but it's obviously wrong.

Test: Ran unit tests on coral.
Change-Id: I96be5b0980c323c3aeafb422fbc06202577604a2
diff --git a/debuggerd/debuggerd_test.cpp b/debuggerd/debuggerd_test.cpp
index 2cf5b18..0737612 100644
--- a/debuggerd/debuggerd_test.cpp
+++ b/debuggerd/debuggerd_test.cpp
@@ -88,7 +88,7 @@
     struct sigaction old_sigaction;                                \
     struct sigaction new_sigaction = {};                           \
     new_sigaction.sa_handler = [](int) {};                         \
-    if (sigaction(SIGALRM, &new_sigaction, &new_sigaction) != 0) { \
+    if (sigaction(SIGALRM, &new_sigaction, &old_sigaction) != 0) { \
       err(1, "sigaction failed");                                  \
     }                                                              \
     alarm(seconds);                                                \