arch-kirkwood: Ethernet port macro returning incorrect address

Modified the arch-kirkwood header so KWGBE_PORT_SERIAL_CONTROL1_REG(x)
returns the correct address.

Originally calling KWGBE_PORT_SERIAL_CONTROL1_REG(1) returned the
address for port 0 and vice versa.

Doesn't have any knock on effects to the u-boot code as the only
time they're used is to do the same function to both addresses

Signed-off-by: Luke Lowrey <luke@chamsys.co.uk>
Acked-by: Prafulla Wadaskar <Prafulla@marvell.com>
Acked-by: Heiko Schocher <hs@denx.de>