iwlwifi: pcie: don't disable the busmaster DMA clock for family 8000

Disabling the clocks is a standard procedure while stopping the
device. On family 8000 however, disabling the bus master DMA clock
increases the NIC's power consumption.

To fix this, skip this call if the device family is
IWL_DEVICE_FAMILY_8000.

Signed-off-by: Avri Altman <avri.altman@intel.com>
Reviewed-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>