CHROMIUM: usb: gadget: f_accessory: add .raw_request callback

After this upstream commit: 3c86726c,
.raw_request is mandatory in hid_ll_driver structure, hence add an empty
raw_request() function.

BUG=chrome-os-partner:49140
TEST=none

Change-Id: Idd0bbe6960aad2c557376e4a24827d7e1df8e023
Signed-off-by: Mark Kuo <mkuo@nvidia.com>
Reviewed-on: https://chromium-review.googlesource.com/321038


Commit-Ready: Andrew Bresticker <abrestic@chromium.org>
Tested-by: Andrew Bresticker <abrestic@chromium.org>
Reviewed-by: Andrew Bresticker <abrestic@chromium.org>