wrong hex conversion

[DanDejy]

https://github.com/avrxml/asf/blame/68cddb46ae5ebc24ef8287a8d4c61a6efa5e2848/common/components/wifi/winc1500/http_downloader_example/iot/http/http_client.c#L955

module->resp.read_length=module->resp.read_length*0x10+ buffer-'a';
should be
module->resp.read_length=module->resp.read_length0x10+ *buffer-'a' + 10;