s3fb: use new start address register

Use "new" start address register 0x69 (bits 16-20) instead of "old" 0x31
(bits 16-17) and 0x51 (bits 18-19). This is needed for panning to work
correctly on Trio3D/2X cards (and does no harm on other ones).

Signed-off-by: Ondrej Zary <linux@rainbow-software.org>
Acked-by: Ondrej Zajicek <santiago@crfreenet.org>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>