ipw2100: minor cleanups

From: Adrian Bunk <bunk@stusta.de>

This patch contains the following possible cleanups:
- make needlessly global code static
- remove the unused IPW_DEBUG_ENABLED

Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: Jiri Benc <jbenc@suse.cz>