staging: r8188eu: convert aes_cipher() to void

The function aes_cipher() returns always _SUCCESS and its callers
do not use the return value. So we can convert the return type to
void and get rid of another use of _SUCCESS.

Tested-by: Philipp Hortmann <philipp.g.hortmann@gmail.com> # Edimax N150
Signed-off-by: Michael Straube <straube.linux@gmail.com>
Link: https://lore.kernel.org/r/20221111083733.3144-2-straube.linux@gmail.com


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