Don't build invensense_hal when working with prebuilt sensor libraries

Change-Id: Ibef5b8bce47b58ff22f287b622122d7e9dd69917
diff --git a/libsensors/Android.mk b/libsensors/Android.mk
index 3745631..06c01e3 100644
--- a/libsensors/Android.mk
+++ b/libsensors/Android.mk
@@ -16,6 +16,8 @@
 
 LOCAL_PATH := $(call my-dir)
 
+ifneq ($(BOARD_USES_GENERIC_INVENSENSE),false)
+
 # InvenSense fragment of the HAL
 include $(CLEAR_VARS)
 
@@ -42,3 +44,5 @@
 LOCAL_PRELINK_MODULE := false
 
 include $(BUILD_SHARED_LIBRARY)
+
+endif