[PATCH] Fix ipw2200 set wrong power parameter causing firmware error

The power mode can only be set 0~5 to firmware. Otherwise there will be a
firmware error generated. This patch fixed the invalid power mode requested
by driver.

Signed-off-by: Zhu Yi <yi.zhu@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>