Staging: winbond: implement prepare_multicast and fix API usage

This patch adds a prepare_multicast callback for the winbond driver
to properly receive mc_count in ->configure_filter.

This also fixes incompatible pointer assignment build errors because
->configure_filter had changed.

This is build tested only, but that's more than the original code received.

Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>