au1000_eth.c: use ether_crc() from <linux/crc32.h>

since the au1000 driver already selects the CRC32 routines, simply replace
the internal ether_crc() implementation with the semantically equivalent
one from <linux/crc32.h>

Signed-off-by: Herbert Valerio Riedel <hvr@gnu.org>
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>