staging: wilc1000: return error code directly in host_int_set_mac_chnl_num

There is no need to pass the error code to the variable 'result'.
Just return the error directly when error occurs.
Return 0 at the end of this function when error is not happened.

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