[CustomOp] Register VocabParallelEmbedding instead of overwrite forward (#2515)

### What this PR does / why we need it?
Register VocabParallelEmbedding instead of overwrite forward

### Does this PR introduce _any_ user-facing change?
N/A

### How was this patch tested?
CI passed with new added/existing test.

- vLLM version: v0.10.1.1
- vLLM main:
644d57d531

---------

Signed-off-by: Icey <1790571317@qq.com>

tests/ut/test_utils.py

@@ -289,13 +289,13 @@ class TestUtils(TestBase):
         # ascend custom op is not registered
         utils.register_ascend_customop()
         # should call register_oot three
-        self.assertEqual(mock_customop.register_oot.call_count, 9)
+        self.assertEqual(mock_customop.register_oot.call_count, 10)
         self.assertTrue(utils._ASCEND_CUSTOMOP_IS_REIGISTERED)
 
         # ascend custom op is already registered
         utils.register_ascend_customop()
         # should not register_oot again, thus only called three in this ut
-        self.assertEqual(mock_customop.register_oot.call_count, 9)
+        self.assertEqual(mock_customop.register_oot.call_count, 10)
 
 
 class TestProfileExecuteDuration(TestBase):