Fix typo with package bisector switch_to_good script

Fix error where cros_pkg_switch_to_good.sh was using the bad build files
if passed a file argument.

Test=Switch to good verification passed with cros_pkg bisector

Change-Id: Ie2d5e1e741ceb97ba05d6f827161d12c103d9e48
Reviewed-on: https://chrome-internal-review.googlesource.com/262466
Commit-Ready: Cassidy Burden <cburden@google.com>
Tested-by: Cassidy Burden <cburden@google.com>
Reviewed-by: Caroline Tice <cmtice@google.com>
diff --git a/binary_search_tool/cros_pkg/cros_pkg_switch_to_good.sh b/binary_search_tool/cros_pkg/cros_pkg_switch_to_good.sh
index b0d07a3..cd4c2ed 100755
--- a/binary_search_tool/cros_pkg/cros_pkg_switch_to_good.sh
+++ b/binary_search_tool/cros_pkg/cros_pkg_switch_to_good.sh
@@ -20,7 +20,7 @@
 
   while read pkg
   do
-    sudo cp ${BAD_BUILD}/packages/$pkg ${WORK_BUILD}/packages/$pkg
+    sudo cp ${GOOD_BUILD}/packages/$pkg ${WORK_BUILD}/packages/$pkg
     status=$?
     if [[ ${status} -ne 0 ]] ; then
       echo "Failed to copy ${pkg} to work build tree."