rtl818x: fix potential use after free

entry is released via usb_put_urb just after calling usb_submit_urb.
However, entry is used if the submission fails, resulting in a use after
free bug. The patch fixes this.

Signed-off-by: Pan Bian <bianpan2016@163.com>
ACKed-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>