qcacld-3.0: Add fallthrough comment in hdd_sme_roam_callback()

In hdd_sme_roam_callback() there is a switch statement where the logic
for case eCSR_ROAM_CANCELLED falls through to the next case. Add a
fallthrough comment to explicitly document that this is the desired
behavior as opposed to a missing break statement.

Change-Id: Ic5fd5c92d7ab421a60d56dfc7761578b554349c6
CRs-Fixed: 2233180

core/hdd/src/wlan_hdd_assoc.c

@@ -4714,6 +4714,7 @@ hdd_sme_roam_callback(void *pContext, struct csr_roam_info *roam_info,
 		break;
 	case eCSR_ROAM_CANCELLED:
 		hdd_debug("****eCSR_ROAM_CANCELLED****");
+		/* fallthrough */
 	case eCSR_ROAM_ASSOCIATION_FAILURE:
 		qdf_ret_status = hdd_association_completion_handler(adapter,
 								    roam_info,