usb: gadget: f_qdss: Fix unclocked access during connect in qdss mode

For the scenario when usb cable is connected followed by quick disconnect
in qdss composition, qdss driver will queue connect work as part of
qdss_set_alt(). This results in crash if connect work is scheduled after
USB enters low power mode.

Fix the issue by checking whether usb is disconnected or not
and if it is already disconnected, then return from qdss connect_work.

CRs-Fixed: 718015
Change-Id: If55bc6813ceabe03a027d40675c360e013ae1bf5
Signed-off-by: Saket Saurabh <ssaurabh@codeaurora.org>