USB: gadget: f_qdss: Add proper checks in usb_qdss_close()

On qdsss channel close, driver is dequeuing endless request without
checking whether qdss is active or not. This might crash if qdss channel
is closed when non QDSS composition is active. Fix the issue by having
proper checks and if qdss is not active, just return without performing
dequeue operation.

Change-Id: I667ea843f77794e9384c22ece218853331751db6
Signed-off-by: Vijayavardhan Vennapusa <vvreddy@codeaurora.org>