rtlwifi: rtl8821ae: Simplify loading of WOWLAN firmware

The existing method for loading both normal and WOWLAN firmware for the
device duplicates a lot of code. This solution is much cleaner.

Signed-off-by: Troy Tan <troy_tan@realsil.com.cn>
Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>