iwlwifi: Execute runtime calibration always

Runtime DC calibration was previously conditional. Remove this
behaviour, as new devices support runtime DC calibration,
while older devices ignore the runtime DC calibration request.

This patch addresses low TX throughput issues seen with the 6205.

Signed-off-by: Meenakshi Venkataraman <meenakshi.venkataraman@intel.com>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>