[AWQ] Remove Code to obtain Merge Node (#3621)

### Changes

Remove Code to obtain Merge Node. Instead directly get the merge node
from the match nodes.

### Reason for changes

`Matmul1 -> mul -> Matmul2` pattern was causing an error when the
precision for `Matmul1` was FP32. The first matmul node was not being
found in `all_weight_params`.

According to my experiments, in both the conditions for patterns
`MatMul->Multiply->MatMul` and `Act->MatMul or Act->Multiply->MatMul` we
essentially do the same task of obtaining the first node from the
matched list of nodes.

### Tests

Category | Job | Status | Job Number | Notes
-- | -- | -- | -- | --
GH Examples | Examples | Pass| <a
href="https://github.com/openvinotoolkit/nncf/actions/runs/16972167283">382</a>
|
GH WC | Weights Compression | Pass | <a
href="https://github.com/openvinotoolkit/nncf/actions/runs/16972170869">137</a>
|

Perplexity Evaluation:
Compression Settings: Ratio=0.8, Hessian Input Activation, backup_mode
NONE
Evaluation Settings: limit 10(evaluate with only 10 samples in lm_eval)
Model: microsoft/Phi-3-mini-128k-instruct

| Branch | AWQ | Accuracy |
|--------|--------|--------|
Develop Branch | No | 11.157 |
Develop Branch | Yes | 11.0583 |
After Change | Yes | 11.0583 |

### Related tickets

172326

Author: anzr299

src/nncf/quantization/algorithms/weight_compression/awq.py

@@ -365,15 +365,7 @@ def _get_awq_data(
             if target_node.node_name in awq_data:
                 continue
 
-            nncf_node = graph.get_node_by_key(match[0])
-
-            if self._backend_entity.is_node_with_weights(nncf_node, graph):  # pattern MatMul->Multiply->MatMul
-                merge_node_names = []
-                for weight_op_friendly_name, _ in self._backend_entity.get_weight_names_and_port_ids(nncf_node, graph):
-                    merge_node_names.append(weight_op_friendly_name)
-                merge_node = all_weight_params[name_mapping[merge_node_names[-1]]].node_with_weight
-            else:  # pattern Act->MatMul or Act->Multiply->MatMul
-                merge_node = nncf_node
+            merge_node = graph.get_node_by_key(match[0])
 
             awq_data[target_node.node_name] = AWQCompressionInfo(weight_params, target_node, merge_node)
         return awq_data