fix Struct's setter arity

https://github.com/ruby/ruby/pull/5131/files#diff-b2553d23e6b1fe76e20608d06c25f6acca06279100f1a9c24febcd79a82fac3cR2689

1 files changed, 1 insertions, 1 deletions

diff --git a/proc.c b/proc.c
index d0451244ce..cff8e9e7af 100644
--- a/proc.c
+++ b/proc.c
@@ -2684,7 +2684,7 @@ method_def_min_max_arity(const rb_method_definition_t *def, int *max)
             return 0;
           case OPTIMIZED_METHOD_TYPE_STRUCT_ASET:
             *max = 1;
-            return 0;
+            return 1;
 	  default:
 	    break;
 	}