UDC: Correct cleaning out memory for string descriptors

BUG=chrome-os-partner:41687
BRANCH=None
TEST=Compiles successfully and fastboot devices reports correct serial
number even after re-connection.

Change-Id: I1348c33f354d11e3c29ccd9da9948cfbeb60aa9e
Signed-off-by: Furquan Shaikh <furquan@google.com>
Reviewed-on: https://chromium-review.googlesource.com/281192
Trybot-Ready: Furquan Shaikh <furquan@chromium.org>
Tested-by: Furquan Shaikh <furquan@chromium.org>
Reviewed-by: Patrick Georgi <pgeorgi@chromium.org>
Commit-Queue: Furquan Shaikh <furquan@chromium.org>
1 file changed