bosch_bmi160: fix build breakage from gyro cal

Change-Id: I606286460862f5e495ca152f5282f596de4e9d64
diff --git a/firmware/src/drivers/bosch_bmi160/bosch_bmi160.c b/firmware/src/drivers/bosch_bmi160/bosch_bmi160.c
index 9c4ab98..6cf4116 100644
--- a/firmware/src/drivers/bosch_bmi160/bosch_bmi160.c
+++ b/firmware/src/drivers/bosch_bmi160/bosch_bmi160.c
@@ -631,9 +631,11 @@
             NANOHUB_INT_NONWAKEUP, 20) },
 };
 
+#ifdef GYRO_CAL_ENABLED
 static bool newGyroBiasAvailable(void) {
   return false;
 }
+#endif
 
 static void time_init(void) {
     time_sync_init(&mTask.gSensorTime2RTC);