mod_image_for_recovery: fix local for decrypt_stateful

Remove local from a variable defined at the script's top level.
Otherwise, when run with --decrypt_stateful fails with
"local: can only be used in a function".

BUG=none
TEST=create recovery image with decrypt_stateful flag

Change-Id: I56b68c80ed9efb6f4b6e8badbfbd88220262eb06
Reviewed-on: https://chromium-review.googlesource.com/703991
Commit-Ready: Andrey Pronin <apronin@chromium.org>
Tested-by: Andrey Pronin <apronin@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
diff --git a/mod_image_for_recovery.sh b/mod_image_for_recovery.sh
index e8d7294..ba92883 100755
--- a/mod_image_for_recovery.sh
+++ b/mod_image_for_recovery.sh
@@ -423,7 +423,7 @@
 
 if [ $FLAGS_decrypt_stateful -eq $FLAGS_TRUE ]; then
   stateful_mnt=$(mktemp -d)
-  local partition_num_state=$(get_image_partition_number \
+  partition_num_state=$(get_image_partition_number \
     "${RECOVERY_IMAGE}" "STATE")
   offset=$(partoffset "${RECOVERY_IMAGE}" "${partition_num_state}")
   sudo mount -o loop,offset=$(( offset * 512 )) \