staging: r8188eu: mark _rtw_free_sta_priv as void

_rtw_free_sta_priv() always returns _SUCCESS and it's return value
isn't checked either.
So it makes sense to mark it as void instead of u32.

Signed-off-by: Vihas Makwana <makvihas@gmail.com>
Link: https://lore.kernel.org/r/20220213173424.39935-1-makvihas@gmail.com


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