qcacld-3.0: Replace is_dp_link_valid with dp_link null check

As a part of vdev destroy is_dp_link_valid can return failure,
since the interface maybe down. This will lead to memory leak
since the dp_link memory won't be freed.

Fix this by replacing is_dp_link_valid with dp_link null check.

Change-Id: Ief03c1e42d62b4b89f1414f0c5642e592ee39fa2
CRs-Fixed: 3750214

components/dp/core/src/wlan_dp_main.c

@@ -2027,7 +2027,7 @@ void wlan_dp_link_cdp_vdev_delete_notification(void *context)
 	uint8_t found = 0;
 
 	/* dp_link will not be freed before this point. */
-	if (!is_dp_link_valid(dp_link))
+	if (!dp_link)
 		return;
 
 	dp_info("dp_link %pK id %d", dp_link, dp_link->link_id);