fix: aidl --checkapi fails even when old/new APIs are the same

The failure was because the return value of check_api which is bool is
returned as the exit code. Fixing the bug by returning 0 when the result
is true.

Test: aidl --checkapi build/api/test-piece-1/current.aidl
build/api/test-piece-1/current.aidl && echo success
shows "success"

Change-Id: I503b0883e2a1e7629fe68e6ec09fdf280ecdb0a2
diff --git a/main.cpp b/main.cpp
index c933ac0..ffc30a1 100644
--- a/main.cpp
+++ b/main.cpp
@@ -49,7 +49,7 @@
     case Options::Task::DUMP_API:
       return android::aidl::dump_api(options, io_delegate) ? 0 : 1;
     case Options::Task::CHECK_API:
-      return android::aidl::check_api(options, io_delegate);
+      return android::aidl::check_api(options, io_delegate) ? 0 : 1;
     default:
       LOG(FATAL) << "aidl: internal error" << std::endl;
       return 1;