fix: Maintain Same Rate Throughout Sales Cycle doesn't work

Issue #29976 was partly fixed by #32923 but the problem still persists.
The reason is because an incorrect fieldname was passed to the
`validate_rate_with_reference_doc` method.
This commit fixes it

(cherry picked from commit 97ddfcf)

erpnext/selling/doctype/quotation/test_quotation.py

@@ -30,6 +30,19 @@ def test_make_sales_order_terms_copied(self):
 
 		self.assertTrue(sales_order.get("payment_schedule"))
 
+	def test_maintain_rate_in_sales_cycle_is_enforced(self):
+		from erpnext.selling.doctype.quotation.quotation import make_sales_order
+
+		quotation = frappe.copy_doc(test_records[0])
+		quotation.transaction_date = nowdate()
+		quotation.valid_till = add_months(quotation.transaction_date, 1)
+		quotation.insert()
+		quotation.submit()
+
+		sales_order = make_sales_order(quotation.name)
+		sales_order.items[0].rate = 1
+		self.assertRaises(frappe.ValidationError, sales_order.save)
+
 	def test_make_sales_order_with_different_currency(self):
 		from erpnext.selling.doctype.quotation.quotation import make_sales_order
 

erpnext/selling/doctype/sales_order/sales_order.py

@@ -194,7 +194,7 @@ def validate_with_previous_doc(self):
 		)
 
 		if cint(frappe.db.get_single_value("Selling Settings", "maintain_same_sales_rate")):
-			self.validate_rate_with_reference_doc([["Quotation", "prev_docname", "quotation_item"]])
+			self.validate_rate_with_reference_doc([["Quotation", "prevdoc_docname", "quotation_item"]])
 
 	def update_enquiry_status(self, prevdoc, flag):
 		enq = frappe.db.sql(