rtlwifi: rtl8192cu: Fix deadlock

Prevent code from calling itself indirectly, causing the driver to hang
and consume 100% CPU.

Without this fix, the following script can bring down a single CPU
system:
```
while true; do
  rmmod rtl8192cu
  modprobe rtl8192cu
done
```

Signed-off-by: Reto Schneider <code@reto-schneider.ch>
ACKed-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200622132113.14508-2-code@reto-schneider.ch