iwlwifi: iwl-eeprom-parse: Fix 'struct iwl_eeprom_enhanced_txpwr's header

Fixes the following W=1 kernel build warning(s):

 drivers/net/wireless/intel/iwlwifi/iwl-eeprom-parse.c:340: warning: cannot understand function prototype: 'struct iwl_eeprom_enhanced_txpwr '

Cc: Johannes Berg <johannes.berg@intel.com>
Cc: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Cc: Luca Coelho <luciano.coelho@intel.com>
Cc: Intel Linux Wireless <linuxwifi@intel.com>
Cc: Kalle Valo <kvalo@codeaurora.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: linux-wireless@vger.kernel.org
Cc: netdev@vger.kernel.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20201126133152.3211309-9-lee.jones@linaro.org