net: neterion: fix doc warnings in s2io.c

Add description for may_sleep to fix the W=1 warnings:

  drivers/net/ethernet/neterion/s2io.c:1110: warning: Function parameter or member 'may_sleep' not described in 'init_tti'
  drivers/net/ethernet/neterion/s2io.c:3335: warning: Function parameter or member 'may_sleep' not described in 'wait_for_cmd_complete'
  drivers/net/ethernet/neterion/s2io.c:4881: warning: Function parameter or member 'may_sleep' not described in 's2io_set_multicast'

Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>