staging: r8188eu: convert rtw_p2p_setDN to return void

rtw_p2p_setDN always returns 0 and it's return value is not used.
Convert it to return void.

Suggested-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Abdun Nihaal <abdun.nihaal@gmail.com>
Link: https://lore.kernel.org/r/fe4a9f0176c96ec327342c793de1f55c89d16768.1643466748.git.abdun.nihaal@gmail.com


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