iwlwifi: dvm: fix chain noise calibration

First step of chain noise calibration process had disable flag
check inverted. Chain noise calibration never started because
of this.

Tested on intel 5300 with two antennas attached. The driver
correctly disabled one chain.

Cc: stable@vger.kernel.org
Signed-off-by: Nikolay Martynov <mar.kolya@gmail.com>
Reviewed-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>