iwlwifi: enable DC calibration

From: Abhijeet Kolekar <abhijeet.kolekar@intel.com>

For 6X50 DC calibration needs to be initialized
else uCode will run an endless loop.
Enbale DC calibration in hw config.

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