iwlwifi: remove IWL_FW_DBG_DOMAIN macro

This is used to initialize the default value, but refers back
to the value itself, essentially leading to a
	val = val
assignment at init time ... that's useless, remove it and use
_NODEF.

Change-Id: I725923016563c34ce2fa057bf7c12984e1041c49
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>