staging: r8188eu: change mlme handlers to void

The mlme handlers that are called from mgt_dispatcher return an error
code. mgt_dispatcher doesn't check this error code, we can remove it and
change the handler functions to void.

For now, make only the minimum changes to the handlers for removing the
error codes. If handlers can be simplified, that'll be done it separate
patches.

Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Tested-by: Philipp Hortmann <philipp.g.hortmann@gmail.com> # Edimax N150
Link: https://lore.kernel.org/r/20221024081417.66441-13-martin@kaiser.cx


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