qcacmn: Access wlan_crypto_cipher structure if key->valid flag is set

Access wlan_crypto_cipher structure if the key and cipher_table's
are valid. Also, added changes to avoid dangling pointer accessing
after deleting key.

Change-Id: Ia9a5942c9597f03eb1707d149797f33760eeac21

umac/cmn_services/crypto/src/wlan_crypto_global_api.c

@@ -1427,6 +1427,7 @@ QDF_STATUS wlan_crypto_delkey(struct wlan_objmgr_vdev *vdev,
 	/* Zero-out local key variables */
 	qdf_mem_zero(key, sizeof(struct wlan_crypto_key));
 	qdf_mem_free(key);
+	key = NULL;
 
 ret_rel_ref:
 	if (peer)
@@ -1765,6 +1766,12 @@ QDF_STATUS wlan_crypto_decap(struct wlan_objmgr_vdev *vdev,
 			goto err;
 		}
 	}
+
+	if (!key->valid || !key->cipher_table) {
+		status = QDF_STATUS_E_INVAL;
+		goto err;
+	}
+
 	/* if tkip, is counter measures enabled, then drop the frame */
 	cipher_table = (struct wlan_crypto_cipher *)key->cipher_table;
 	status = cipher_table->decap(key, wbuf, tid, hdrlen);