usb-ccid: move header size check

Move up header size check, so we can use header fields in sanity checks
(in followup patches).  Also reword the debug message.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-id: 1487250819-23764-3-git-send-email-kraxel@redhat.com
