iwlwifi: don't double free the interrupt in failure path

When the driver can't get the HW ready, we would release
the interrupt twice which made the kernel complain loudly.

Cc: stable@vger.kernel.org
Reported-by: Brian Cockrell <brian.cockrell@intel.com>
Tested-by: Brian Cockrell <brian.cockrell@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>