qcacmn: dp: 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: I443da8d7f5e1771dceb3386c4458b0da6a5e9476
CRs-Fixed: 3218236

dp/wifi3.0/dp_tx_desc.h

@@ -264,19 +264,19 @@ dp_tx_adjust_flow_pool_state(struct dp_soc *soc,
 		soc->pause_cb(pool->flow_pool_id,
 			      WLAN_NETIF_PRIORITY_QUEUE_OFF,
 			      WLAN_DATA_FLOW_CTRL_PRI);
-		/* fallthrough */
+		fallthrough;
 
 	case FLOW_POOL_VO_PAUSED:
 		soc->pause_cb(pool->flow_pool_id,
 			      WLAN_NETIF_VO_QUEUE_OFF,
 			      WLAN_DATA_FLOW_CTRL_VO);
-		/* fallthrough */
+		fallthrough;
 
 	case FLOW_POOL_VI_PAUSED:
 		soc->pause_cb(pool->flow_pool_id,
 			      WLAN_NETIF_VI_QUEUE_OFF,
 			      WLAN_DATA_FLOW_CTRL_VI);
-		/* fallthrough */
+		fallthrough;
 
 	case FLOW_POOL_BE_BK_PAUSED:
 		soc->pause_cb(pool->flow_pool_id,