iwlwifi: don't fail power set when calibration is not done yet

This patch doesn't fail power save setting when calibration is
not done yet. The new power index is registered and will
be evaluated again anyway upon calibration completion.

This patch also eliminates WARN_ON in mac80211 hw_config during
initialization

Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>