Fix typo

This was producing a number of unused source warnings for prebuilt files
using LOCAL_SRC_FILES_<arch>.

Change-Id: I48d1face7baf642f3ef17f957448ccb73788765f
diff --git a/core/prebuilt_internal.mk b/core/prebuilt_internal.mk
index 6d9ded4..7598768 100644
--- a/core/prebuilt_internal.mk
+++ b/core/prebuilt_internal.mk
@@ -26,7 +26,7 @@
 else
   ifdef LOCAL_SRC_FILES_$($(my_prefix)$(LOCAL_2ND_ARCH_VAR_PREFIX)ARCH)
     my_prebuilt_src_file := $(LOCAL_PATH)/$(LOCAL_SRC_FILES_$($(my_prefix)$(LOCAL_2ND_ARCH_VAR_PREFIX)ARCH))
-    LOCAL_SRC_FILES_$($(my_prefix)$(LOCAL_2ND_ARCH_VAR_PREFIX)ARCH)) :=
+    LOCAL_SRC_FILES_$($(my_prefix)$(LOCAL_2ND_ARCH_VAR_PREFIX)ARCH) :=
   else
     ifdef LOCAL_SRC_FILES_$(my_32_64_bit_suffix)
       my_prebuilt_src_file := $(LOCAL_PATH)/$(LOCAL_SRC_FILES_$(my_32_64_bit_suffix))