staging: wilc1000: set_channel: fix data type of s32Error

This patch changes data type of s32Error variable from s32 to int
because return type of this function is int.

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