staging: wilc1000: fix return type of wilc_set_power_mgmt

This patch changes return type of wilc_set_power_mgmt from s32 to int.
The result variable gets return value from wilc_mq_send that has return
type of int. It should be changed return type of this function as well
as data type of result variable.

Signed-off-by: Chaehyun Lim <chaehyun.lim@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>