usb: f_qdss: dequeue pending requests upon qdss close

When qdss_close is called the pending requests sent to the
controller are not stopped and as a result the completion
call back can occur at any time. If the qdss bridge driver
frees the requests before the completion callback may result
in use after free. Call dequeue on the pending requests in
qdss close so that the requests are terminated instantly.

Change-Id: I2752a598e8b104a6803064343743f591adc924e4
Signed-off-by: Elson Roy Serrao <eserrao@codeaurora.org>