qcacld-3.0: tdls: 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: Icdb1590b51cf172728c3b484f05d20c49e68c38e
CRs-Fixed: 3217422

os_if/tdls/src/wlan_cfg80211_tdls.c

@@ -977,6 +977,7 @@ void wlan_cfg80211_tdls_event_callback(void *user_data,
 	case TDLS_EVENT_ANTENNA_SWITCH:
 		tdls_priv->tdls_antenna_switch_status = ind->status;
 		complete(&tdls_priv->tdls_antenna_switch_comp);
+		break;
 	default:
 		break;
 	}