wifi: rtw89: parse PHY status only when PPDU is to_self

Without this fix, some non-self packets are used to count CFO (center
frequency offset), and average CFO has unstable variation. Then, it causes
unexpected performance.

Signed-off-by: Eric Huang <echuang@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20221005083212.45683-3-pkshih@realtek.com