wifi: rtl8xxxu: Clean up some messy ifs

Add some new members to rtl8xxxu_fileops and use them instead of
checking priv->rtl_chip.

Signed-off-by: Bitterblue Smith <rtl8821cerfe2@gmail.com>
Reviewed-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/e24a5534-6e33-cfb9-0634-0caf4646513f@gmail.com