patch 9.1.0887: Wrong expression in sign.c

Problem:  Wrong expression in sign.c
          (after v9.1.0885)
Solution: remove the duplicate expression

Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/sign.c b/src/sign.c
index 2ae74e4..e997a77 100644
--- a/src/sign.c
+++ b/src/sign.c
@@ -2819,7 +2819,7 @@
 
     if (dict != NULL)
     {
-        dictitem_T *di = di = dict_find(dict, (char_u *)"buffer", -1);
+        dictitem_T *di = dict_find(dict, (char_u *)"buffer", -1);
         if (di != NULL)
         {
             buf = get_buf_arg(&di->di_tv);