wifi: rtw89: chan: Use swap() in rtw89_swap_sub_entity()

Use existing swap() function instead of keeping duplicate source code.

./drivers/net/wireless/realtek/rtw89/chan.c:2336:32-33: WARNING opportunity for swap().

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Closes: https://bugzilla.openanolis.cn/show_bug.cgi?id=9174


Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Link: https://msgid.link/20240529020244.129027-1-jiapeng.chong@linux.alibaba.com