staging: r8188eu: exit for deauth from unknown station

If we receive a deauth message from an unknown station, we can drop this
message and exit immediately. Reorder the code to make this clearer, don't
wrap everything in an if statement.

Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Tested-by: Philipp Hortmann <philipp.g.hortmann@gmail.com> # Edimax N150
Acked-by: Pavel Skripkin <paskripkin@gmail.com>
Link: https://lore.kernel.org/r/20221015152440.232281-7-martin@kaiser.cx


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