nanohub: isl29034: fix build error when DEBUG not defined

Test: make -C variant/argonkey DEBUG=
Change-Id: Id2c96ff1cd27647890e19d7d4ef8fa70b3e7fb05
Signed-off-by: Ben Fennema <fennema@google.com>
diff --git a/firmware/os/drivers/intersil_isl29034/isl29034.c b/firmware/os/drivers/intersil_isl29034/isl29034.c
index 6eec4a7..95df33e 100644
--- a/firmware/os/drivers/intersil_isl29034/isl29034.c
+++ b/firmware/os/drivers/intersil_isl29034/isl29034.c
@@ -35,6 +35,10 @@
 #define ISL29034_DBG_ENABLED                    1
 #endif
 
+#ifndef ISL29034_DBG_ENABLED
+#define ISL29034_DBG_ENABLED                    0
+#endif /* ISL29034_DBG_ENABLED */
+
 #define ISL29034_APP_VERSION                    1
 
 #define ISL29034_REG_CMD_1                      0x00