build/make/Android.mk: s/armv8/arm64/

the configure target is arm64-android-gcc which generates .mk files of
the same form

Change-Id: I08af3a54ef203b1496d185a0f8c8fe702881a173

build/make/Android.mk

@@ -71,7 +71,7 @@ ifeq ($(TARGET_ARCH_ABI),armeabi-v7a)
   include $(CONFIG_DIR)libs-armv7-android-gcc.mk
   LOCAL_ARM_MODE := arm
 else ifeq  ($(TARGET_ARCH_ABI),arm64-v8a)
-  include $(CONFIG_DIR)libs-armv8-android-gcc.mk
+  include $(CONFIG_DIR)libs-arm64-android-gcc.mk
   LOCAL_ARM_MODE := arm
 else ifeq ($(TARGET_ARCH_ABI),x86)
   include $(CONFIG_DIR)libs-x86-android-gcc.mk