DM9000: Remove cal_CRC() and use ether_crc_le instead

Remove the cal_CRC as this is basically wrappering the
ether_crc_le function, and is only being used by the
multicast hash table functions.

Signed-off-by: Ben Dooks <ben-linux@fluff.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>