wifi: rtl8xxxu: Fix the 40 MHz subchannel for RTL8192EU, RTL8723BU

wifi: rtl8xxxu: Fix the 40 MHz subchannel for RTL8192EU, RTL8723BU

rtl8xxxu_gen2_config_channel() was missing the subchannel setting.
This function is used by RTL8192EU and RTL8723BU.

This change seems to make no difference in my testing on channel 13
with either chip.

Signed-off-by: Bitterblue Smith <rtl8821cerfe2@gmail.com>
Reviewed-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Link: https://patch.msgid.link/a5de8d39-45c1-4667-ab4c-7109de6eb13d@gmail.com