[PATCH] ipw2100: Fix `iwpriv set_power` error

iwpriv <iface> set_power [0~6] can be used for ipw2100. '0' indicates
off and '6' indicates auto. 1~5 are the actual power levels.

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