drivers: entropy: bt_hci: Add missing netbuf unref

bt_hci_cmd_send_sync() requires the caller to unref the buffer that is
sent back as a response. Add the missing call to net_buf_unref()
accordingly.

Signed-off-by: Carles Cufi <carles.cufi@nordicsemi.no>

drivers/entropy/entropy_bt_hci.c

@@ -39,6 +39,8 @@ static int entropy_bt_get_entropy(const struct device *dev,
 		/* Copy random data into buffer */
 		rp = (void *)rsp->data;
 		memcpy(buffer, rp->rand, req);
+
+		net_buf_unref(rsp);
 		buffer += req;
 		length -= req;
 	}