staging: wlan-ng: fix ODEBUG bug in prism2sta_disconnect_usb

staging: wlan-ng: fix ODEBUG bug in prism2sta_disconnect_usb

BugLink: https://bugs.launchpad.net/bugs/1870604
commit a1f165a6b738f0c9d744bad4af7a53909278f5fc upstream.

We should cancel hw->usb_work before kfree(hw).

Reported-by: syzbot+6d2e7f6fa90e27be9d62@syzkaller.appspotmail.com
Signed-off-by: Qiujun Huang <hqjagain@gmail.com>
Cc: stable <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/1585120006-30042-1-git-send-email-hqjagain@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>