usb: gadget: Prevent endless_req being freed from disconnect_work

Commit 05c1d8c ("usb: gadget: Prevent use after free in qdss connect
& close") provided a fix for preventing dwc3 driver from accessing
usb_request after dequeue. However, while doing usb disconnect &
connecting again due to endless_req being NULL the BAM2BAM
communication fails. So for the subsequent time the transfer fails.

Fix this by removing endless_req check from disconnect_work.

Change-Id: I8411cb2ae854fb9e2fa15ff89670035ff645289d
Signed-off-by: Udipto Goswami <ugoswami@codeaurora.org>