phy: phy-mt65xx-usb3: fix test fail of HS receiver sensitivity

when use the default value 8 of RG_USB20_SQTH, the HS receiver
sensitivity test of HQA will fail, set it as 2 to fix up the
issue.

Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>