iwlwifi: mvm: BT Coex - don't enable MULTI_PRIO_LUT

This feature isn't supported by the firmware (yet).
Note that settingt he values to BT_CFG_CMD is harmless if
the validity bit is clear - so keep the configuration
values in BT_CFG_CMD, but clear the validity bit until thes
feature is enabled in the firmware.

Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>