usb: misc: uss720: fix uninitialized variable rlen

Smatch reports the following error: uninitialized symbol 'rlen'

drivers/usb/misc/uss720.c:514 parport_uss720_epp_write_data() error
drivers/usb/misc/uss720.c:575 parport_uss720_ecp_write_data() error
drivers/usb/misc/uss720.c:593 parport_uss720_ecp_read_data() error
drivers/usb/misc/uss720.c:626 parport_uss720_write_compat() error

The root cause is, the failure of usb_bulk_msg leads to the
uninitialized variable rlen in printk function.

Fix this by initializing rlen with zero.

Signed-off-by: Dongliang Mu <mudongliangabcd@gmail.com>
Link: https://lore.kernel.org/r/20220903100004.2874741-1-dzm91@hust.edu.cn
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>