extract_utils: Set customvendor.mk name when available

Change-Id: I06eac71446983da815a8b46b65d02902c4b4f072
diff --git a/build/tools/extract_utils.sh b/build/tools/extract_utils.sh
index 706ec7e..8632cf8 100755
--- a/build/tools/extract_utils.sh
+++ b/build/tools/extract_utils.sh
@@ -83,7 +83,7 @@
         VNDNAME="$DEVICE"
     fi
 
-    export PRODUCTMK="$OMNI_ROOT"/"$OUTDIR"/device-vendor.mk
+    export PRODUCTMK="$OMNI_ROOT"/"$OUTDIR"/"$VNDNAME"-vendor.mk
     export ANDROIDMK="$OMNI_ROOT"/"$OUTDIR"/Android.mk
     export BOARDMK="$OMNI_ROOT"/"$OUTDIR"/BoardConfigVendor.mk