servo: fix wrong number of arguments to ctrl_u()

When running `dut-control kb_press:ctrl_u` for board squawks I get the
error: Problem with ['kb_press:ctrl_u'] :: ctrl_u() takes exactly 1
argument (2 given). Fix the method ctrl_u() in Servod class and in
USBkm232Handler keyboard handler and add the duration as the second
argument.

BUG=None
TEST=`servod --board=squawks &; dut-control kb_press:ctrl_u` works

Change-Id: I4776713338c652120d56a1291a7d2424ddcd7fc5
Reviewed-on: https://chromium-review.googlesource.com/336090
Commit-Ready: Victor Dodon <printesoi@chromium.org>
Tested-by: Victor Dodon <printesoi@chromium.org>
Reviewed-by: Todd Broch <tbroch@chromium.org>
2 files changed