DM9000: Fix revision ID for DM9000B

The DM9000B revision ID is 0x1A, not 0x1B as set in the curernt
dm9000.h header.

Fix bug reported by Paolo Zebelloni.

Signed-off-by: Ben Dooks <ben@simtec.co.uk>
Signed-off-by: Simtec Linux Team <linux@simtec.co.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>