diag: Fix sending log on demand command to peripherals

Diag driver forms the response to log on demand request and sends
the response to the tools without forwarding to the peripherals.
Make changes to send the request to the peripherals first before
sending the response in both regular usb and dci channels.

Change-Id: I22cd826d82b03b23e41113f73c1099e8f36275ef
Signed-off-by: Ravi Aravamudhan <aravamud@codeaurora.org>