KCM: fix memory leak

`ldb_msg_add_value()` makes a copy under the hood, so there is no need
to make intermediate copy of `secret` argument.
This copy - `secret_val.data` - was left hanging on `sss_sec_ctx`, effectively
resulting in a memory leak.

This is a backport of SSSD#7823

:fixes:'sssd_kcm' memory leak was fixed.

src/responder/kcm/secrets/secrets.c

@@ -953,7 +953,7 @@ errno_t sss_sec_put(struct sss_sec_req *req,
                     size_t secret_len)
 {
     struct ldb_message *msg;
-    struct ldb_val secret_val;
+    const struct ldb_val secret_val = { .length = secret_len, .data = secret };
     int ret;
 
     if (req == NULL || secret == NULL) {
@@ -1002,13 +1002,6 @@ errno_t sss_sec_put(struct sss_sec_req *req,
         goto done;
     }
 
-    secret_val.length = secret_len;
-    secret_val.data = talloc_memdup(req->sctx, secret, secret_len);
-    if (!secret_val.data) {
-        ret = ENOMEM;
-        goto done;
-    }
-
     ret = ldb_msg_add_value(msg, SEC_ATTR_SECRET, &secret_val, NULL);
     if (ret != EOK) {
         DEBUG(SSSDBG_OP_FAILURE,
@@ -1050,7 +1043,7 @@ errno_t sss_sec_update(struct sss_sec_req *req,
                        size_t secret_len)
 {
     struct ldb_message *msg;
-    struct ldb_val secret_val;
+    const struct ldb_val secret_val = { .length = secret_len, .data = secret };
     int ret;
 
     if (req == NULL || secret == NULL) {
@@ -1099,13 +1092,6 @@ errno_t sss_sec_update(struct sss_sec_req *req,
         goto done;
     }
 
-    secret_val.length = secret_len;
-    secret_val.data = talloc_memdup(req->sctx, secret, secret_len);
-    if (!secret_val.data) {
-        ret = ENOMEM;
-        goto done;
-    }
-
     /* FIXME - should we have a lastUpdate timestamp? */
     ret = ldb_msg_add_empty(msg, SEC_ATTR_SECRET, LDB_FLAG_MOD_REPLACE, NULL);
     if (ret != LDB_SUCCESS) {