usb: gadget: qdss: Fix control transport handling

commit 2ff2189 ("USB: QTI_DPL: Add support for QTI control with
DPL") added support for control transports to enable the DPL
feature, however the checks added in usb_qdss_connect_work()
and usb_qdss_disconnect_work() incorrectly return if the
ctrl_xports is unspecified. This breaks QDSS since this should
be treated as an optional parameter.

Change-Id: Ifc6051009b1a4d016948156ac0a65ab3923b6043
Signed-off-by: Jack Pham <jackp@codeaurora.org>