build: Fix failed to assign a module name different with it's file name to a prebuilt module

Build system can not find the dependent library if assigning a
multi-prebuilt which module name is different with it's library
file name as following:
    PREBUILT_LIBS := libabc_debug:libabc.a

Change-Id: I05bdc8cebcabf74195198e3cefa1b8923f87d406
diff --git a/core/multi_prebuilt.mk b/core/multi_prebuilt.mk
index be60e2f..bc85cea 100644
--- a/core/multi_prebuilt.mk
+++ b/core/multi_prebuilt.mk
@@ -69,7 +69,11 @@
   $(if $(7), \
     $(eval LOCAL_BUILT_MODULE_STEM := $(7)) \
    , \
-    $(eval LOCAL_BUILT_MODULE_STEM := $(notdir $(LOCAL_SRC_FILES))) \
+    $(if $(word 2,$(tw)), \
+      $(eval LOCAL_BUILT_MODULE_STEM := $(LOCAL_MODULE)$(suffix $(LOCAL_SRC_FILES))) \
+     , \
+      $(eval LOCAL_BUILT_MODULE_STEM := $(notdir $(LOCAL_SRC_FILES))) \
+     ) \
    ) \
   $(eval LOCAL_MODULE_SUFFIX := $(suffix $(LOCAL_SRC_FILES))) \
   $(if $(filter user,$(TARGET_BUILD_VARIANT)), \