compat-wireless: fix make install

compat-wireless: fix make install

This issue was introduced via this patch:

commit 802ea47e6316aea285f2c30d95763dd7c320eec1
Author: Rick Farina <sidhayn@gmail.com>
Date:   Fri Feb 24 21:28:40 2012 -0500

    compat-wireless: replace modprobe -l with functional equivilent

Fix the regression by properly using brackets on the
conditional check and also guaranteeing we output something
upon success. Not sure how this could have worked.

Signed-off-by: Luis R. Rodriguez <mcgrof@frijolero.org>