staging: serqt_usb2: remove retval initialisation in qt_tiocmget and qt_tiocmset
in qt_tiocmset,
the retval gets assigned if we have a valid serial pointer in the critical section
(between mutex_lock and _unlock) of the code, no need to initialise this variable.
the same retval assignment follows in the qt_tiocmget function also, so remove the
initialisation here too.