qcacmn: Fix implicit-fallthrough compile error casued by gcc 9.3

Compiling with gcc 9.3 will cause many implicit-fallthrough
compile errors.

Fix is to add keyword fallthrough to resolve such compile error.

Change-Id: I2e7dd1525861d951e3be44f6665e149499f0f5d6
CRs-Fixed: 2785178

dp/wifi3.0/dp_main.c

@@ -8752,6 +8752,7 @@ static QDF_STATUS dp_get_vdev_param(struct cdp_soc_t *cdp_soc, uint8_t vdev_id,
 		break;
 	case CDP_ENABLE_MCAST_EN:
 		val->cdp_vdev_param_mcast_en = vdev->mcast_enhancement_en;
+		break;
 	case CDP_ENABLE_HLOS_TID_OVERRIDE:
 		val->cdp_vdev_param_hlos_tid_override =
 			    dp_vdev_get_hlos_tid_override((struct cdp_vdev *)vdev);