rtlwifi: fix scan channel 1 fail after IPS

If there is no connection, driver will enter IPS state. Meanwhile, it
fails to scan channel 1 by the command 'iw dev wlan0 scan freq 2412',
because hardware channel setting lose after IPS. Thus, restore channel
setting from hw->conf.channel set by last rtl_op_config().

Signed-off-by: Tim Lee <timlee@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>