qcacld-3.0: umac: Replace fallthrough comment with attribute

-Wimplicit-fallthrough is being enabled by default. Some compilers
such as clang require the attribute instead of just a fallthrough comment.

Change-Id: I7a04c8727121f58a5d6dcd575446c9acedea164b
CRs-Fixed: 3216248

components/umac/mlme/connection_mgr/dispatcher/src/wlan_cm_roam_api.c

@@ -2445,7 +2445,7 @@ cm_roam_event_handler(struct roam_offload_roam_event *roam_event)
 		if (roam_event->rso_timer_stopped)
 			wlan_cm_rso_stop_continue_disconnect(roam_event->psoc,
 						roam_event->vdev_id, true);
-		/* fallthrough */
+		fallthrough;
 	case ROAM_REASON_INVALID:
 		cm_handle_roam_offload_events(roam_event);
 		break;

components/umac/mlme/connection_mgr/dispatcher/src/wlan_cm_roam_ucfg_api.c

@@ -392,7 +392,7 @@ QDF_STATUS ucfg_cm_check_ft_status(struct wlan_objmgr_pdev *pdev,
 				   mlme_priv->connect_info.ft_info.ft_state);
 			break;
 		}
-		/* fallthrough */
+		fallthrough;
 	default:
 		mlme_debug("Unhandled state:%d",
 			   mlme_priv->connect_info.ft_info.ft_state);