rtlwifi: rtl8821ae: Fix incorrect returned values

In commit bd421dab ("rtlwifi: rtl8821ae: Convert macros that set
descriptor"), all the routines that get fields from a descriptor
were changed to return signed integer values. This is incorrect for the
routines that get the entire 32-bit word. In this case, an unsigned
quantity is required.

Fixes: bd421dab ("rtlwifi: rtl8821ae: Convert macros that set descriptor")
Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>