Fix issue: 'sx_port_mapping_t' object has no attribute 'slot_id' (#9835)

- Why I did it
Fix issue: 'sx_port_mapping_t' object has no attribute 'slot_id'. sx_port_mapping_t only has attribute slot.

- How I did it
Change slot_id to slot.

- How to verify it
Manual test

Author: Junchao-Mellanox

platform/mellanox/mlnx-platform-api/sonic_platform/sfp_event.py

@@ -367,7 +367,7 @@ def on_pmpe(self, fd_p):
                         label_port = slot_id * DeviceDataManager.get_linecard_max_port_count() + x + 1
                         break
 
-                    if port_attributes.port_mapping.slot_id == slot_id:
+                    if port_attributes.port_mapping.slot == slot_id:
                         x += 1
 
                 if label_port is not None: