byte-cntr: ensure usbch to be ready

Ensure usbch is ready before usb bypass start to avoid usbch is NULL
in usb_read_work_fn().

Change-Id: I0b932f1713a2d49424860728e79e3684122b4e40
Signed-off-by: Yuanfang Zhang <zhangyuanfang@codeaurora.org>