usb: f_qdss: Fix watchdog bark issue on wait_for_completion

The coresight driver is freeing up d_req as part of notify
from write_complete. Accessing write_done form qdss_close,
wait_for_completion will be stuck there causing watchdog
bark.

Fix this by making f_qdss independent of coresight driver
from initializing complete. Initialization of completion
now occurs from alloc_req.

Change-Id: Ie6b1cd445ed6bb38c1a555f6c4c41068090e4fac
Signed-off-by: Udipto Goswami <ugoswami@codeaurora.org>
Signed-off-by: Mayank Rana <mrana@codeaurora.org>