Fix the following warning:

drivers/net/wireless/realtek/rtl818x/rtl8187/rtl8225.c:609:17: warning:
‘rtl8225z2_tx_power_ofdm’ defined but not used
 static const u8 rtl8225z2_tx_power_ofdm[] = {
Acked-by: Hin-Tak Leung <htl10@users.sourceforge.net>
Acked-by: Larry Finger <Larry.Finger@lwfinger.net>
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: ChenTao <chentao107@huawei.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200513011754.28432-1-chentao107@huawei.com