wifi: rtw89: drop invalid TX rate report of legacy rate

Somehow, firmware could report invalid TX rate, and we consider the
invalid rate as 0 that will make a wrong decision. So, drop invalid
reports, and also suppress the warning message.

Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20220610072610.27095-9-pkshih@realtek.com