qosConfig should account for portSpeedCableLength (sonic-net#8699)

Fixed typo in initializing qosConfig when testing "wm_buf_pool_lossy". This will fix the KeyError: 'wm_buf_pool_lossy' problem.

Summary:
Fixes sonic-net#8698

Fix initialization of qosConfig when testing "wm_buf_pool_lossy" as for
some platforms, the parameters are indexed by portSpeedCableLength.
This will fix the KeyError: 'wm_buf_pool_lossy' problem.

tests/qos/test_qos_sai.py

@@ -919,7 +919,8 @@ def testQosSaiBufferPoolWatermark(
             fillMin = qosConfig[bufPool]["pkts_num_fill_ingr_min"]
             buf_pool_roid = ingressLosslessProfile["bufferPoolRoid"]
         elif "wm_buf_pool_lossy" in bufPool:
-            qosConfig = dutQosConfig["param"]
+            baseQosConfig = dutQosConfig["param"]
+            qosConfig = baseQosConfig.get(portSpeedCableLength, baseQosConfig)
             triggerDrop = qosConfig[bufPool]["pkts_num_trig_egr_drp"]
             fillMin = qosConfig[bufPool]["pkts_num_fill_egr_min"]
             buf_pool_roid = egressLossyProfile["bufferPoolRoid"]