phy-sun4i-usb: Change disconnect threshold value for sun6i

The allwinner SDK uses a value of 3 for the disconnect threshold setting on
sun6i, do the same in the kernel.

In my previous experience with sun5i problems getting the threshold right
is important to avoid usb2 devices being unplugged sometimes going unnoticed.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>