staging: rtl8712u: Remove dummy reset-resume callback

An USB wireless dongle uses rtl8712u stops working after system
suspend/resume.

When a USB device lost its power during suspend, the USB core knows the
power was lost and a reset-resume or a re-probe is required. But rtl8712u
provides a dummy reset-resume callback, which gets called and renders
the device dead after resume.

So remove the reset-resume call back, if power was lost during suspend,
let the USB core unbind and probe the device to solve the issue.

Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>