Fix memory corruption due to BLE multi-adv macro

INST_ID_IDX_MAX macro was not protected with parenthesis, resulting
in incorrect calculation of the size needed to allocate memory for
the client_if map.

Change-Id: Ib3591f4f9ac7288f2191e9078a71aab431ca7130
diff --git a/btif/include/btif_gatt_multi_adv_util.h b/btif/include/btif_gatt_multi_adv_util.h
index fd1426f..f9d4a8d 100644
--- a/btif/include/btif_gatt_multi_adv_util.h
+++ b/btif/include/btif_gatt_multi_adv_util.h
@@ -25,7 +25,7 @@
 
 #define CLNT_IF_IDX 0
 #define INST_ID_IDX 1
-#define INST_ID_IDX_MAX INST_ID_IDX + 1
+#define INST_ID_IDX_MAX (INST_ID_IDX + 1)
 #define INVALID_ADV_INST -1
 #define STD_ADV_INSTID 0