rtlwifi: rtl8192de: Fix firmware header endian issues

This driver is converted to use the common firmware header struct.
Because the old header definition failed to indicate that the multi-byte
entries should be little endian, several problems were thus exposed.
These are fixed.

Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>