Fix misc-macro-parentheses warnings.

Bug: 28705665
Change-Id: I1ad468741c6f117817099d2ba87374dce2b776a9
diff --git a/drm/common/IDrmManagerService.cpp b/drm/common/IDrmManagerService.cpp
index f2e14b6..1614e26 100644
--- a/drm/common/IDrmManagerService.cpp
+++ b/drm/common/IDrmManagerService.cpp
@@ -33,7 +33,7 @@
 
 #include "IDrmManagerService.h"
 
-#define INVALID_BUFFER_LENGTH -1
+#define INVALID_BUFFER_LENGTH (-1)
 #define MAX_BINDER_TRANSACTION_SIZE ((1*1024*1024)-(4096*2))
 
 using namespace android;