[nrf fromtree] bluetooth: host: gatt: destroy key after hash calc completes

To generate the GATT Database Hash characteristic, the function
`db_hash_setup` is called. It allocates an entry for the AES key that will
be used in the CMAC calculation. Next, `db_hash_update` is called to feed
all GATT database entries into the hash. Finally, `db_hash_finish`
produces the resulting hash.

However, the AES key entry allocated in `db_hash_setup` was not being
destroyed after the hash generation completed. This caused a memory
leak, eventually leading to the error `PSA_ERROR_INSUFFICIENT_MEMORY`
(`-134`).

This commit fixes the issue by destroying the allocated AES key after
the GATT Database Hash calculation is complete, by calling
`psa_destroy_key` in `db_hash_finish`.

Signed-off-by: Pavel Vasilyev <[email protected]>
(cherry picked from commit bcdd74d)

Author: PavelVPV

subsys/bluetooth/host/gatt.c

@@ -755,6 +755,8 @@ static int db_hash_finish(struct gen_hash_state *state)
 	size_t mac_length;
 	psa_status_t ret = psa_mac_sign_finish(&(state->operation), db_hash.hash, 16, &mac_length);
 
+	psa_destroy_key(state->key);
+
 	if (ret != PSA_SUCCESS) {
 		LOG_ERR("CMAC finish failed %d", ret);
 		return -EIO;