staging: ks7010: change return value of ks_wlan_do_power_save function

This commit change return value of ks_wlan_do_power_save function
from int to void. This function is just returning zero and return
value is not being checked also, so it is nonsense to return an
integer.

Signed-off-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>