iwlwifi: fix merge sequence: exit on error before state change

The intention behind the original patch:
"iwlwifi: fix possible read attempt on ucode that is not available"
was to exit before any state is changed. Due to its submission directly
to 2.6.24 it was not clear how this relates to the latest iwlwifi work.

This patch does exactly the same as the previous patch, just earlier to
prevent any state from being changed if there is an error.

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