USB: f_qdss: Fix crash issue during connect_work

If it happens that usb_qdss_close() gets called before
completion of qdss_connect_work(), there is a chance that endless
request being accessed in connect_work(), which will be freed in
usb_qdss_close(). Fix that issue by having proper check for
endless request under spinlock protection.

Change-Id: Ied14137e01bf685547c093b907484b4dee583fda
Signed-off-by: Vijayavardhan Vennapusa <vvreddy@codeaurora.org>