qdss_bridge: fix stuck issue when driver remove

Only the memory written to usb needs to wait for write complete
when removed driver or modem ssr happened. The "used" member is
used to mark the state of memory written to usb.

Change-Id: Ia1755a6c38f8419c5282347744a3d8f3d3b58ad7
Signed-off-by: Yuanfang Zhang <zhangyuanfang@codeaurora.org>