sunxi: Fix wrong serial console setup in Forfun Q88DB tablet

sunxi: Fix wrong serial console setup in Forfun Q88DB tablet

The Forfun Q88DB tablet was unbootable since commit
b6006baf9c2553543e3384983d23d95efbf24fa6 ("sunxi: Move all
boards to the driver-model"). Appears that this is caused
by the wrong serial console setup in the SPL. The serial
console should use PG3/PG4 pins according to the FEX file.

Signed-off-by: Siarhei Siamashka <siarhei.siamashka@gmail.com>
Acked-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>