Use frozen copy of ion.h for this code.

Use the ion.h copy in system/core/libion since it's frozen.

Test: Builds.
Change-Id: Iabbd89691a9ca6b25fde320180b80aba3769b6c7
diff --git a/moorefield_hdmi/Android.mk b/moorefield_hdmi/Android.mk
index 8903585..79097bb 100644
--- a/moorefield_hdmi/Android.mk
+++ b/moorefield_hdmi/Android.mk
@@ -96,6 +96,10 @@
     $(TARGET_OUT_HEADERS)/libttm \
     frameworks/native/include/media/openmax
 
+# Use the frozen version of ion.h.
+LOCAL_C_INCLUDES += \
+    $(TOP)/system/core/libion/kernel-headers \
+
 ifeq ($(TARGET_SUPPORT_HDMI_PRIMARY),true)
    LOCAL_CFLAGS += -DINTEL_SUPPORT_HDMI_PRIMARY
 endif