usb: cdc-wdm:Fix loss of data due to autosuspend

The guarding flag must be set and tested under spinlock
and cleared before the URBs are resubmitted in resume.

Signed-off-by: Oliver Neukum <neukum@b1-systems.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>