fix amount not updated when change rate in material request (#39606)

* fix amount not updated when change rate in material request

* make code consistent
diff --git a/erpnext/stock/doctype/material_request/material_request.js b/erpnext/stock/doctype/material_request/material_request.js
index 03fe20b..e80218a 100644
--- a/erpnext/stock/doctype/material_request/material_request.js
+++ b/erpnext/stock/doctype/material_request/material_request.js
@@ -429,6 +429,9 @@
 
 	rate: function(frm, doctype, name) {
 		const item = locals[doctype][name];
+		item.amount = flt(item.qty) * flt(item.rate);
+		frappe.model.set_value(doctype, name, "amount", item.amount);
+		refresh_field("amount", item.name, item.parentfield);
 		frm.events.get_item_data(frm, item, false);
 	},