git.el: Pass an explicit argument to enable smerge-mode.

Without argument the mode is toggled, which would do the wrong thing
if the file was already open.

Signed-off-by: Alexandre Julliard <julliard@winehq.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/emacs/git.el

@@ -1058,7 +1058,7 @@ Return the list of files that haven't been handled."
   (let ((info (ewoc-data (ewoc-locate git-status))))
     (find-file (git-fileinfo->name info))
     (when (eq 'unmerged (git-fileinfo->state info))
-      (smerge-mode))))
+      (smerge-mode 1))))
 
 (defun git-find-file-other-window ()
   "Visit the current file in its own buffer in another window."