iwlagn: set CSR register for 6050g2 devices

For 6050g2 devices driver needs to set a special bit to CSR register
so that uCode can do things correctly in calibration routines.

Signed-off-by: Shanyu Zhao <shanyu.zhao@intel.com>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>