staging/serqt_usb2: Refactor qt_status_change_check() in serqt_usb2.c

Modify qt_status_change_check() and delete qt_status_change().

Signed-off-by: YAMANE Toshiaki <yamanetoshi@gmail.com>
Acked-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>