staging: r8188eu: remove return value from on_action_public_vendor

The only caller of on_action_public_vendor does not check the return
value. We can make it a void function.

Tested-by: Philipp Hortmann <philipp.g.hortmann@gmail.com> # Edimax N150
Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Link: https://lore.kernel.org/r/20221030173326.1588647-11-martin@kaiser.cx


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