rtw88: 8723de: adjust the LTR setting

The LTR mechanism enables PCIE Endpoints to report the service latency
requirements and CPU will enter appropriate sleep state to save power
based on the LTR value.

8723de provides two registers to config the LTR, and the original setting
is too short for CPU to ente sleep state. The patch adjust the LTR setting.

Signed-off-by: Chin-Yen Lee <timlee@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20210113014342.3615-1-pkshih@realtek.com