checker: fix struct field fntype value call (#19067)

vlib/v/checker/fn.v

@@ -1779,7 +1779,7 @@ fn (mut c Checker) method_call(mut node ast.CallExpr) ast.Type {
 						// cannot hide interface expected type to make possible to pass its interface type automatically
 						earg_types << if targ.idx() != param.typ.idx() { param.typ } else { targ }
 					} else {
-						earg_types << targ
+						earg_types << param.typ
 					}
 					param_share := param.typ.share()
 					if param_share == .shared_t

vlib/v/tests/struct_field_fn_call_test.v

@@ -0,0 +1,18 @@
+struct Foo {
+	f fn (Foo) int = dummy
+}
+
+fn dummy(s Foo) int {
+	return 22
+}
+
+fn (mut s Foo) fun() int {
+	return s.f(s)
+}
+
+fn test_struct_field_fn_call() {
+	mut s := Foo{}
+	ret := s.fun()
+	println(ret)
+	assert ret == 22
+}