Fix misc-macro-parentheses warnings.

Bug: 28705665
Change-Id: Ib7520c64075a652eb0b15483f36383c4632624d1
diff --git a/libril/ril.cpp b/libril/ril.cpp
index 30b4220..52f46a7 100644
--- a/libril/ril.cpp
+++ b/libril/ril.cpp
@@ -86,7 +86,7 @@
 #define RESPONSE_UNSOLICITED 1
 
 /* Negative values for private RIL errno's */
-#define RIL_ERRNO_INVALID_RESPONSE -1
+#define RIL_ERRNO_INVALID_RESPONSE (-1)
 
 // request, response, and unsolicited msg print macro
 #define PRINTBUF_SIZE 8096