zsh_completion: fix trailing carriage return spoiling tag completion stable

zsh_completion: fix trailing carriage return spoiling tag completion

This was giving the following error:

 % hg up 2.5-r<Tab>
 (eval):1: bad substitution
 % hg up 2.5-r

--- a/contrib/zsh_completion	Fri Mar 29 15:27:11 2013 -0700
+++ b/contrib/zsh_completion	Fri Mar 29 18:45:07 2013 -0700
@@ -176,7 +176,7 @@
   do
     tags+=(${tag/ #[0-9]#:*})
   done
-  (( $#tags )) && _describe -t tags 'tags' tags
+  (( $#tags )) && _describe -t tags 'tags' tags
 }
 _hg_bookmarks() {
   typeset -a bookmark bookmarks