wifi: rtw88: 8821cu: Fix firmware upload fail

wifi: rtw88: 8821cu: Fix firmware upload fail

RTL8822CU, RTL8822BU, and RTL8821CU need an extra register write after
reading and writing certain addresses.

Without this, the firmware upload fails approximately more than 50% of
the time.

Tested with RTL8811CU (Tenda U9 V2.0) which is the same as RTL8821CU
but without Bluetooth.

Fixes: a82dfd33d123 ("wifi: rtw88: Add common USB chip support")
Signed-off-by: Bitterblue Smith <rtl8821cerfe2@gmail.com>
Acked-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://msgid.link/f12ed39d-28e8-4b8b-8d22-447bcf295afc@gmail.com