staging: rtl8192u: Fix use after free in ieee80211_rx()

We cannot dereference the "skb" pointer after calling
ieee80211_monitor_rx(), because it is a use after free.

Fixes: 8fc8598e ("Staging: Added Realtek rtl8192u driver to staging")
Signed-off-by: Dan Carpenter <error27@gmail.com>
Link: https://lore.kernel.org/r/Y33BArx3k/aw6yv/@kili


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>