rtw88: raise LPS threshold to 50, for less power consumption

The LPS threshold was set to 2, means driver will leave LPS
mode if there is more than 2 frames TX/RX for every 2 seconds.
This makes driver enter/leave LPS frequently even if we just
"ping -i1" to the others.

Apparently we do not want to leave LPS mode if there is only
some background traffics or web surfing. By experiment, set
this to 50 is a more reasonable value to lower the over all
power consumption.

Signed-off-by: Yan-Hsuan Chuang <yhchuang@realtek.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>