coresight: byte-cntr: Free USB requests when disconnected

When receiving USB_QDSS_CONNECT notification, 255 USB requests
are allocated before starting the worker thread to begin writing
to USB QDSS function driver. Conversely when USB_QDSS_DISCONNECT
is received, these requests need to be freed. Without doing so,
besides causing a slow memory leak, the existing requests would get
incorrectly re-used and may fail if the USB endpoint changed due
to a composition switch.

Change-Id: I328e110719fab374827ac69c8b60274f65ec81e2
Signed-off-by: Jack Pham <jackp@codeaurora.org>