patch 8.2.2573: Vim9: using inalid pointer for error message

Problem:    Vim9: using inalid pointer for error message.
Solution:   Use the right pointer. (closes #7921)
diff --git a/src/eval.c b/src/eval.c
index 6b12a97..1ad6339 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -3130,7 +3130,7 @@
 	 */
 	if (evaluate && in_vim9script() && !IS_WHITE_OR_NUL((*arg)[1]))
 	{
-	    error_white_both(p, 1);
+	    error_white_both(*arg, 1);
 	    clear_tv(rettv);
 	    return FAIL;
 	}